/*************************************************************************
 *
 * Copyright (c) 2012-2014 Kohei Yoshida
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 ************************************************************************/

#include "multi_type_vector_macro.hpp"

#include <stdexcept>
#include <memory>

namespace mdds {

namespace detail {

inline void throw_block_position_not_found(
    const char* method_sig, int line, size_t pos, size_t block_size, size_t container_size)
{
    std::ostringstream os;
    os << method_sig << "#" << line << ": block position not found! (logical pos="
        << pos << ", block size=" << block_size << ", logical size=" << container_size << ")";
    throw std::out_of_range(os.str());
}

template<typename T>
T mtv_advance_position(const T& pos, int steps)
{
    T ret = pos;

    if (steps > 0)
    {
        while (steps > 0)
        {
            if (ret.second + steps < ret.first->size)
            {
                // element is still in the same block.
                ret.second += steps;
                break;
            }
            else
            {
                steps -= (ret.first->size - ret.second);
                ++ret.first;
                ret.second = 0;
            }
        }
    }
    else
    {
        while (steps < 0)
        {
            if (static_cast<int>(ret.second) >= -steps)
            {
                ret.second += steps;
                break;
            }
            else
            {
                steps += ret.second + 1;
                --ret.first;
                ret.second = ret.first->size - 1;
            }
        }
    }

    return ret;
}

}

MDDS_MTV_DEFINE_ELEMENT_CALLBACKS(double, mtv::element_type_numeric, 0.0, mtv::numeric_element_block)
MDDS_MTV_DEFINE_ELEMENT_CALLBACKS(std::string, mtv::element_type_string, std::string(), mtv::string_element_block)
MDDS_MTV_DEFINE_ELEMENT_CALLBACKS(short, mtv::element_type_short, 0, mtv::short_element_block)
MDDS_MTV_DEFINE_ELEMENT_CALLBACKS(unsigned short, mtv::element_type_ushort, 0, mtv::ushort_element_block)
MDDS_MTV_DEFINE_ELEMENT_CALLBACKS(int, mtv::element_type_int, 0, mtv::int_element_block)
MDDS_MTV_DEFINE_ELEMENT_CALLBACKS(unsigned int, mtv::element_type_uint, 0, mtv::uint_element_block)
MDDS_MTV_DEFINE_ELEMENT_CALLBACKS(long, mtv::element_type_long, 0, mtv::long_element_block)
MDDS_MTV_DEFINE_ELEMENT_CALLBACKS(unsigned long, mtv::element_type_ulong, 0, mtv::ulong_element_block)
MDDS_MTV_DEFINE_ELEMENT_CALLBACKS(bool, mtv::element_type_boolean, false, mtv::boolean_element_block)
MDDS_MTV_DEFINE_ELEMENT_CALLBACKS(char, mtv::element_type_char, 0, mtv::char_element_block)
MDDS_MTV_DEFINE_ELEMENT_CALLBACKS(unsigned char, mtv::element_type_uchar, 0, mtv::uchar_element_block)

template<typename _CellBlockFunc, typename _EventFunc>
multi_type_vector<_CellBlockFunc, _EventFunc>::block::block() : m_size(0), mp_data(nullptr) {}

template<typename _CellBlockFunc, typename _EventFunc>
multi_type_vector<_CellBlockFunc, _EventFunc>::block::block(size_type _size) : m_size(_size), mp_data(nullptr) {}

template<typename _CellBlockFunc, typename _EventFunc>
multi_type_vector<_CellBlockFunc, _EventFunc>::block::block(size_type _size, element_block_type* _data) :
    m_size(_size), mp_data(_data) {}

template<typename _CellBlockFunc, typename _EventFunc>
multi_type_vector<_CellBlockFunc, _EventFunc>::block::block(const block& other) :
    m_size(other.m_size), mp_data(other.mp_data) {}

template<typename _CellBlockFunc, typename _EventFunc>
multi_type_vector<_CellBlockFunc, _EventFunc>::block::block(block&& other) :
    m_size(other.m_size), mp_data(other.mp_data)
{
    other.m_size = 0;
    other.mp_data = nullptr;
}

template<typename _CellBlockFunc, typename _EventFunc>
multi_type_vector<_CellBlockFunc, _EventFunc>::block::~block() {}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::block::swap(block& other)
{
    std::swap(m_size, other.m_size);
    std::swap(mp_data, other.mp_data);
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::block::clone_to(block& other) const
{
    other.m_size = m_size;
    if (mp_data)
        other.mp_data = element_block_func::clone_block(*mp_data);
    else
        other.mp_data = nullptr;
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::block&
multi_type_vector<_CellBlockFunc, _EventFunc>::block::operator=(block other)
{
    swap(other);
    return *this;
}

template<typename _CellBlockFunc, typename _EventFunc>
multi_type_vector<_CellBlockFunc, _EventFunc>::blocks_to_transfer::blocks_to_transfer() : insert_index(0) {}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::position_type
multi_type_vector<_CellBlockFunc, _EventFunc>::next_position(const position_type& pos)
{
    position_type ret = pos;
    if (pos.second + 1 < pos.first->size)
    {
        // Next element is still in the same block.
        ++ret.second;
    }
    else
    {
        ++ret.first;
        ret.second = 0;
    }

    return ret;
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::position_type
multi_type_vector<_CellBlockFunc, _EventFunc>::advance_position(const position_type& pos, int steps)
{
    return detail::mtv_advance_position<position_type>(pos, steps);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::const_position_type
multi_type_vector<_CellBlockFunc, _EventFunc>::next_position(const const_position_type& pos)
{
    const_position_type ret = pos;
    if (pos.second + 1 < pos.first->size)
    {
        // Next element is still in the same block.
        ++ret.second;
    }
    else
    {
        ++ret.first;
        ret.second = 0;
    }

    return ret;
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::const_position_type
multi_type_vector<_CellBlockFunc, _EventFunc>::advance_position(const const_position_type& pos, int steps)
{
    return detail::mtv_advance_position<const_position_type>(pos, steps);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::size_type
multi_type_vector<_CellBlockFunc, _EventFunc>::logical_position(const const_position_type& pos)
{
    return pos.first->position + pos.second;
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _Blk>
typename _Blk::value_type
multi_type_vector<_CellBlockFunc, _EventFunc>::get(const const_position_type& pos)
{
    return _Blk::at(*pos.first->data, pos.second);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::begin()
{
    return iterator(m_blocks.begin(), m_blocks.end(), 0, 0);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::end()
{
    size_type start_pos = 0, block_index = 0;
    if (!m_blocks.empty())
    {
        // Get the index and the start row position of the imaginary block after the last block.
        block_index = m_blocks.size();
        start_pos = m_cur_size;
    }
    return iterator(m_blocks.end(), m_blocks.end(), start_pos, block_index);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::const_iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::begin() const
{
    return const_iterator(m_blocks.begin(), m_blocks.end(), 0, 0);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::const_iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::end() const
{
    return const_iterator(m_blocks.end(), m_blocks.end(), 0, 0);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::reverse_iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::rbegin()
{
    return reverse_iterator(m_blocks.rbegin(), m_blocks.rend(), 0, 0);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::reverse_iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::rend()
{
    return reverse_iterator(m_blocks.rend(), m_blocks.rend(), 0, 0);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::const_reverse_iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::rbegin() const
{
    return const_reverse_iterator(m_blocks.rbegin(), m_blocks.rend(), 0, 0);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::const_reverse_iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::rend() const
{
    return const_reverse_iterator(m_blocks.rend(), m_blocks.rend(), 0, 0);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::event_func&
multi_type_vector<_CellBlockFunc, _EventFunc>::event_handler()
{
    return m_hdl_event;
}

template<typename _CellBlockFunc, typename _EventFunc>
const typename multi_type_vector<_CellBlockFunc, _EventFunc>::event_func&
multi_type_vector<_CellBlockFunc, _EventFunc>::event_handler() const
{
    return m_hdl_event;
}

template<typename _CellBlockFunc, typename _EventFunc>
multi_type_vector<_CellBlockFunc, _EventFunc>::multi_type_vector() : m_cur_size(0) {}

template<typename _CellBlockFunc, typename _EventFunc>
multi_type_vector<_CellBlockFunc, _EventFunc>::multi_type_vector(const event_func& hdl) :
    m_hdl_event(hdl), m_cur_size(0) {}

template<typename _CellBlockFunc, typename _EventFunc>
multi_type_vector<_CellBlockFunc, _EventFunc>::multi_type_vector(event_func&& hdl) :
    m_hdl_event(std::move(hdl)), m_cur_size(0) {}

template<typename _CellBlockFunc, typename _EventFunc>
multi_type_vector<_CellBlockFunc, _EventFunc>::multi_type_vector(size_type init_size) : m_cur_size(init_size)
{
    if (!init_size)
        return;

    // Initialize with an empty block that spans from 0 to max.
    m_blocks.emplace_back(init_size);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
multi_type_vector<_CellBlockFunc, _EventFunc>::multi_type_vector(size_type init_size, const _T& value) :
    m_cur_size(init_size)
{
    if (!init_size)
        return;

    element_block_type* data = mdds_mtv_create_new_block(init_size, value);
    m_hdl_event.element_block_acquired(data);
    m_blocks.emplace_back(init_size, data);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
multi_type_vector<_CellBlockFunc, _EventFunc>::multi_type_vector(size_type init_size, const _T& it_begin, const _T& it_end) :
    m_cur_size(init_size)
{
    if (!m_cur_size)
        return;

    size_type data_len = std::distance(it_begin, it_end);
    if (m_cur_size != data_len)
        throw invalid_arg_error("Specified size does not match the size of the initial data array.");

    element_block_type* data = mdds_mtv_create_new_block(*it_begin, it_begin, it_end);
    m_hdl_event.element_block_acquired(data);
    m_blocks.emplace_back(m_cur_size, data);
}

template<typename _CellBlockFunc, typename _EventFunc>
multi_type_vector<_CellBlockFunc, _EventFunc>::multi_type_vector(const multi_type_vector& other) :
    m_cur_size(other.m_cur_size)
{
    // Clone all the blocks.
    m_blocks.reserve(other.m_blocks.size());
    typename blocks_type::const_iterator it = other.m_blocks.begin(), it_end = other.m_blocks.end();
    block tmp;
    for (; it != it_end; ++it)
    {
        it->clone_to(tmp);
        m_blocks.emplace_back(tmp.m_size, tmp.mp_data);
        if (tmp.mp_data)
            m_hdl_event.element_block_acquired(tmp.mp_data);
    }
}

template<typename _CellBlockFunc, typename _EventFunc>
multi_type_vector<_CellBlockFunc, _EventFunc>::~multi_type_vector()
{
    delete_element_blocks(m_blocks.begin(), m_blocks.end());
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set(size_type pos, const _T& value)
{
    size_type start_row = 0;
    size_type block_index = 0;
    if (!get_block_position(pos, start_row, block_index))
        detail::throw_block_position_not_found("multi_type_vector::set", __LINE__, pos, block_size(), size());

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    std::ostringstream os_prev_block;
    dump_blocks(os_prev_block);
#endif

    iterator ret = set_impl(pos, start_row, block_index, value);

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    if (!check_block_integrity())
    {
        cerr << "block integrity check failed in set (" << pos << ")" << endl;
        cerr << "previous block state:" << endl;
        cerr << os_prev_block.str();
        abort();
    }
#endif

    return ret;
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set(const iterator& pos_hint, size_type pos, const _T& value)
{
    size_type start_row = 0;
    size_type block_index = 0;
    get_block_position(pos_hint, pos, start_row, block_index);

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    std::ostringstream os_prev_block;
    dump_blocks(os_prev_block);
#endif

    iterator ret = set_impl(pos, start_row, block_index, value);

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    if (!check_block_integrity())
    {
        cerr << "block integrity check failed in set (" << pos << ")" << endl;
        cerr << "previous block state:" << endl;
        cerr << os_prev_block.str();
        abort();
    }
#endif

    return ret;
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::delete_element_block(block& blk)
{
    if (!blk.mp_data)
        // This block is empty.
        return;

    m_hdl_event.element_block_released(blk.mp_data);
    element_block_func::delete_block(blk.mp_data);
    blk.mp_data = nullptr;
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::delete_element_blocks(
    typename blocks_type::iterator it, typename blocks_type::iterator it_end)
{
    std::for_each(it, it_end,
        [&](block& r)
        {
            delete_element_block(r);
        }
    );
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set_impl(
    size_type pos, size_type start_row, size_type block_index, const _T& value)
{
    element_category_type cat = mdds_mtv_get_element_type(value);

    typename blocks_type::iterator block_pos = m_blocks.begin();
    std::advance(block_pos, block_index);
    block* blk = &*block_pos;
    assert(blk->m_size > 0); // block size should never be zero at any time.

    assert(pos >= start_row);
    size_type pos_in_block = pos - start_row;
    assert(pos_in_block < blk->m_size);

    if (!blk->mp_data)
    {
        // This is an empty block.
        return set_cell_to_empty_block(start_row, block_index, pos_in_block, value);
    }

    assert(blk->mp_data);
    element_category_type blk_cat = mdds::mtv::get_block_type(*blk->mp_data);

    if (blk_cat == cat)
    {
        // This block is of the same type as the cell being inserted.
        size_type i = pos - start_row;
        element_block_func::overwrite_values(*blk->mp_data, i, 1);
        mdds_mtv_set_value(*blk->mp_data, i, value);
        return iterator(block_pos, m_blocks.end(), start_row, block_index);
    }

    assert(blk_cat != cat);

    if (pos == start_row)
    {
        // Insertion point is at the start of the block.
        if (blk->m_size == 1)
            return set_cell_to_block_of_size_one(start_row, block_index, value);

        assert(blk->m_size > 1);
        block* blk_prev = get_previous_block_of_type(block_index, cat);
        if (blk_prev)
        {
            // Append to the previous block.
            size_type offset = blk_prev->m_size;
            blk->m_size -= 1;
            element_block_func::overwrite_values(*blk->mp_data, 0, 1);
            element_block_func::erase(*blk->mp_data, 0);
            blk_prev->m_size += 1;
            mdds_mtv_append_value(*blk_prev->mp_data, value);
            return get_iterator(block_index-1, start_row-offset);
        }

        set_cell_to_top_of_data_block(block_index, value);
        return get_iterator(block_index, start_row);
    }

    if (pos < (start_row + blk->m_size - 1))
    {
        // Insertion point is somewhere in the middle of the block.
        return set_cell_to_middle_of_block(start_row, block_index, pos_in_block, value);
    }

    // Insertion point is at the end of the block.
    assert(pos == (start_row + blk->m_size - 1));
    assert(pos > start_row);
    assert(blk->m_size > 1);

    if (block_index == 0)
    {
        if (m_blocks.size() == 1)
        {
            // This is the only block.  Pop the last value from the
            // previous block, and insert a new block for the cell being
            // inserted.
            set_cell_to_bottom_of_data_block(0, value);
            iterator itr = end();
            --itr;
            return itr;
        }

        block* blk_next = get_next_block_of_type(block_index, cat);
        if (!blk_next)
        {
            // Pop the last cell of the current block, and insert a new block
            // with the new cell.
            set_cell_to_bottom_of_data_block(0, value);
            iterator itr = begin();
            ++itr;
            return itr;
        }

        // Pop the last cell off the current block, and prepend the
        // new cell to the next block.
        element_block_func::overwrite_values(*blk->mp_data, blk->m_size-1, 1);
        element_block_func::erase(*blk->mp_data, blk->m_size-1);
        blk->m_size -= 1;
        mdds_mtv_prepend_value(*blk_next->mp_data, value);
        blk_next->m_size += 1;

        return get_iterator(block_index+1, start_row+blk->m_size);
    }

    assert(block_index > 0);

    if (block_index == m_blocks.size()-1)
    {
        // This is the last block.
        set_cell_to_bottom_of_data_block(block_index, value);
        iterator itr = end();
        --itr;
        return itr;
    }

    block* blk_next = get_next_block_of_type(block_index, cat);
    if (!blk_next)
    {
        // Next block is either empty or of different type than that of the cell being inserted.
        set_cell_to_bottom_of_data_block(block_index, value); // This invalidates m_blocks.
        size_type len = m_blocks[block_index].m_size;
        return get_iterator(block_index+1, start_row+len);
    }

    // Pop the last element from the current block, and prepend the cell
    // into the next block.
    element_block_func::overwrite_values(*blk->mp_data, blk->m_size-1, 1);
    element_block_func::erase(*blk->mp_data, blk->m_size-1);
    blk->m_size -= 1;
    mdds_mtv_prepend_value(*blk_next->mp_data, value);
    blk_next->m_size += 1;

    return get_iterator(block_index+1, start_row+blk->m_size);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::release_impl(
    size_type pos, size_type start_pos, size_type block_index, _T& value)
{
    const block& blk = m_blocks[block_index];

    if (!blk.mp_data)
    {
        // Empty cell block.  There is no element to release.
        mdds_mtv_get_empty_value(value);
        return get_iterator(block_index, start_pos);
    }

    assert(pos >= start_pos);
    assert(blk.mp_data); // data for non-empty blocks should never be nullptr.
    size_type idx = pos - start_pos;
    mdds_mtv_get_value(*blk.mp_data, idx, value);

    // Set the element slot empty without overwriting it.
    return set_empty_in_single_block(pos, pos, block_index, start_pos, false);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set(size_type pos, const _T& it_begin, const _T& it_end)
{
    size_type end_pos = 0;
    if (!set_cells_precheck(pos, it_begin, it_end, end_pos))
        return end();

    size_type block_index1 = 0, start_row1 = 0;
    if (!get_block_position(pos, start_row1, block_index1))
        detail::throw_block_position_not_found("multi_type_vector::set", __LINE__, pos, block_size(), size());

    return set_cells_impl(pos, end_pos, start_row1, block_index1, it_begin, it_end);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set(const iterator& pos_hint, size_type pos, const _T& it_begin, const _T& it_end)
{
    size_type end_pos = 0;
    if (!set_cells_precheck(pos, it_begin, it_end, end_pos))
        return end();

    size_type block_index1 = 0, start_row1 = 0;
    get_block_position(pos_hint, pos, start_row1, block_index1);

    return set_cells_impl(pos, end_pos, start_row1, block_index1, it_begin, it_end);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::push_back(const _T& value)
{
    element_category_type cat = mdds_mtv_get_element_type(value);

    block* blk_last = m_blocks.empty() ? nullptr : &m_blocks.back();
    if (!blk_last || !blk_last->mp_data || cat != get_block_type(*blk_last->mp_data))
    {
        // Either there is no block, or the last block is empty or of
        // different type.  Append a new block.
        size_type block_index = m_blocks.size();
        size_type start_pos = m_cur_size;

        m_blocks.emplace_back(1);
        create_new_block_with_new_cell(m_blocks.back().mp_data, value);
        ++m_cur_size;

        return get_iterator(block_index, start_pos);
    }

    assert(blk_last);
    assert(blk_last->mp_data);
    assert(cat == get_block_type(*blk_last->mp_data));

    // Append the new value to the last block.
    size_type block_index = m_blocks.size() - 1;
    size_type start_pos = m_cur_size - blk_last->m_size;

    mdds_mtv_append_value(*blk_last->mp_data, value);
    ++blk_last->m_size;
    ++m_cur_size;

    return get_iterator(block_index, start_pos);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::push_back_empty()
{
    size_type last_block_size = 0;
    if (!m_blocks.empty())
        last_block_size = m_blocks.back().m_size;

    size_type block_index = m_blocks.size();
    size_type start_pos = m_cur_size;

    if (!append_empty(1))
    {
        // Last empty block has been extended.
        --block_index;
        start_pos -= last_block_size;
    }

    // Get the iterator of the last block.
    typename blocks_type::iterator block_pos = m_blocks.end();
    --block_pos;

    return iterator(block_pos, m_blocks.end(), start_pos, block_index);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::insert(size_type pos, const _T& it_begin, const _T& it_end)
{
    size_type block_index = 0, start_pos = 0;
    if (!get_block_position(pos, start_pos, block_index))
        detail::throw_block_position_not_found("multi_type_vector::insert", __LINE__, pos, block_size(), size());

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    std::ostringstream os_prev_block;
    dump_blocks(os_prev_block);
#endif

    iterator ret = insert_cells_impl(pos, start_pos, block_index, it_begin, it_end);

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    if (!check_block_integrity())
    {
        cerr << "block integrity check failed in insert (" << pos << ")" << endl;
        cerr << "previous block state:" << endl;
        cerr << os_prev_block.str();
        abort();
    }
#endif

    return ret;
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::insert(const iterator& pos_hint, size_type pos, const _T& it_begin, const _T& it_end)
{
    size_type block_index = 0, start_pos = 0;
    get_block_position(pos_hint, pos, start_pos, block_index);

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    std::ostringstream os_prev_block;
    dump_blocks(os_prev_block);
#endif

    iterator ret = insert_cells_impl(pos, start_pos, block_index, it_begin, it_end);

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    if (!check_block_integrity())
    {
        cerr << "block integrity check failed in insert (" << pos << ")" << endl;
        cerr << "previous block state:" << endl;
        cerr << os_prev_block.str();
        abort();
    }
#endif

    return ret;
}

template<typename _CellBlockFunc, typename _EventFunc>
bool multi_type_vector<_CellBlockFunc, _EventFunc>::get_block_position(
    size_type row, size_type& start_row, size_type& block_index) const
{
    for (size_type i = block_index, n = m_blocks.size(); i < n; ++i)
    {
        const block& blk = m_blocks[i];
        if (row < start_row + blk.m_size)
        {
            // Row is in this block.
            block_index = i;
            return true;
        }

        // Specified row is not in this block.
        start_row += blk.m_size;
    }

    return false;
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::get_block_position(
    const const_iterator& pos_hint, size_type pos, size_type& start_row, size_type& block_index) const
{
    start_row = 0;
    block_index = 0;
    if (pos_hint.get_end() == m_blocks.end())
    {
        // Iterator is valid. Get the block position from it unless it's the
        // end position.
        if (pos_hint.get_pos() != pos_hint.get_end())
        {
            start_row = pos_hint->position;
            block_index = pos_hint->__private_data.block_index;
        }
    }

    if (pos < start_row)
    {
        // Position hint is past the insertion position. Reset.
        start_row = 0;
        block_index = 0;
    }

    if (!get_block_position(pos, start_row, block_index))
        detail::throw_block_position_not_found("multi_type_vector::get_block_position", __LINE__, pos, block_size(), size());
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
void multi_type_vector<_CellBlockFunc, _EventFunc>::create_new_block_with_new_cell(element_block_type*& data, const _T& cell)
{
    if (data)
    {
        m_hdl_event.element_block_released(data);
        element_block_func::delete_block(data);
    }

    // New cell block with size 1.
    data = mdds_mtv_create_new_block(1, cell);
    if (!data)
        throw general_error("Failed to create new block.");

    m_hdl_event.element_block_acquired(data);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set_cell_to_middle_of_block(
    size_type start_row, size_type block_index, size_type pos_in_block, const _T& cell)
{
    block& blk_new = set_new_block_to_middle(block_index, pos_in_block, 1, true);
    create_new_block_with_new_cell(blk_new.mp_data, cell);

    // Return the iterator referencing the inserted block.
    block& blk = m_blocks[block_index];
    return get_iterator(block_index+1, start_row+blk.m_size);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
void multi_type_vector<_CellBlockFunc, _EventFunc>::append_cell_to_block(size_type block_index, const _T& cell)
{
    m_blocks[block_index].m_size += 1;
    mdds_mtv_append_value(*m_blocks[block_index].mp_data, cell);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set_cell_to_empty_block(
    size_type start_row, size_type block_index, size_type pos_in_block, const _T& cell)
{
    block* blk = &m_blocks[block_index];

    if (block_index == 0)
    {
        // Topmost block.
        if (m_blocks.size() == 1)
        {
            // this is the only block.
            assert(blk->m_size == m_cur_size);
            if (m_cur_size == 1)
            {
                // This column is allowed to have only one row!
                assert(pos_in_block == 0);
                create_new_block_with_new_cell(blk->mp_data, cell);
                return begin();
            }

            // block has multiple rows.
            if (pos_in_block == 0)
            {
                // Insert into the first cell in block.
                blk->m_size -= 1;
                assert(blk->m_size > 0);

                m_blocks.emplace(m_blocks.begin(), 1);
                blk = &m_blocks[block_index]; // old pointer is invalid.
                create_new_block_with_new_cell(blk->mp_data, cell);
                return begin();
            }

            if (pos_in_block == blk->m_size - 1)
            {
                // Insert into the last cell in block.
                blk->m_size -= 1;
                assert(blk->m_size > 0);

                m_blocks.emplace_back(1);
                blk = &m_blocks.back(); // old pointer is invalid.

                create_new_block_with_new_cell(blk->mp_data, cell);
                iterator ret = end();
                --ret;
                return ret;
            }

            // Insert into the middle of the block.
            return set_cell_to_middle_of_block(start_row, block_index, pos_in_block, cell);
        }

        // This topmost empty block is followed by a non-empty block.

        if (pos_in_block == 0)
        {
            assert(block_index < m_blocks.size()-1);
            if (blk->m_size == 1)
            {
                // Top empty block with only one cell size.
                element_category_type cat = mdds_mtv_get_element_type(cell);
                block* blk_next = get_next_block_of_type(block_index, cat);
                if (blk_next)
                {
                    // Remove this one-cell empty block from the top, and
                    // prepend the cell to the next block.
                    delete_element_block(m_blocks.front());
                    m_blocks.erase(m_blocks.begin());
                    blk = &m_blocks.front(); // old pointer is invalid.
                    blk->m_size += 1;
                    mdds_mtv_prepend_value(*blk->mp_data, cell);
                }
                else
                    create_new_block_with_new_cell(blk->mp_data, cell);
            }
            else
            {
                assert(blk->m_size > 1);
                blk->m_size -= 1;
                m_blocks.emplace(m_blocks.begin(), 1);
                create_new_block_with_new_cell(m_blocks.front().mp_data, cell);
            }

            return begin();
        }

        if (pos_in_block == blk->m_size - 1)
        {
            // Immediately above a non-empty block.
            element_category_type cat = mdds_mtv_get_element_type(cell);
            block* blk_next = get_next_block_of_type(block_index, cat);
            if (blk_next)
            {
                assert(blk->m_size > 1);
                // Shrink this empty block by one, and prepend the cell to the next block.
                blk->m_size -= 1;
                blk_next->m_size += 1;
                mdds_mtv_prepend_value(*blk_next->mp_data, cell);
            }
            else
            {
                blk->m_size -= 1;
                typename blocks_type::iterator it = m_blocks.begin();
                std::advance(it, block_index+1);
                m_blocks.emplace(it, 1);
                blk = &m_blocks[block_index]; // old pointer is invalid.
                block* blk2 = &m_blocks[block_index+1];
                create_new_block_with_new_cell(blk2->mp_data, cell);
            }

            return get_iterator(block_index+1, start_row+blk->m_size);
        }

        // Inserting into the middle of an empty block.
        return set_cell_to_middle_of_block(start_row, block_index, pos_in_block, cell);
    }

    // This empty block is right below a non-empty block.
    assert(block_index > 0 && m_blocks[block_index-1].mp_data != nullptr);

    if (pos_in_block == 0)
    {
        // New cell is right below the non-empty block.
        element_category_type blk_cat_prev = mdds::mtv::get_block_type(*m_blocks[block_index-1].mp_data);
        element_category_type cat = mdds_mtv_get_element_type(cell);
        if (blk_cat_prev == cat)
        {
            // Extend the previous block by one to insert this cell.
            size_type offset = m_blocks[block_index-1].m_size; // for returned iterator

            if (blk->m_size == 1)
            {
                // Check if we need to merge with the following block.
                if (block_index == m_blocks.size()-1)
                {
                    // Last block.  Delete this block and extend the previous
                    // block by one.
                    delete_element_block(m_blocks[block_index]);
                    m_blocks.pop_back();
                    append_cell_to_block(block_index-1, cell);
                }
                else
                {
                    // Block exists below.
                    block* blk_next = get_next_block_of_type(block_index, blk_cat_prev);
                    if (blk_next)
                    {
                        assert(blk_next->mp_data); // Empty block must not be followed by another empty block.

                        // We need to merge the previous and next blocks, then
                        // delete the current and next blocks.  Be sure to
                        // resize the next block to zero to prevent the
                        // transferred cells to be deleted.
                        block& blk_prev = m_blocks[block_index-1];

                        // Check if the next block is bigger.
                        if (blk_prev.m_size < blk_next->m_size)
                        {
                            // Prepend the new item to the next block, then
                            // prepend the content of the previous block and
                            // release both previous and current blocks.

                            // Increase the size of block and prepend the new cell
                            blk_next->m_size += 1;
                            mdds_mtv_prepend_value(*blk_next->mp_data, cell);

                            // Preprend the content of previous block to next one
                            element_block_func::prepend_values_from_block(*blk_next->mp_data, *blk_prev.mp_data, 0, blk_prev.m_size);
                            blk_next->m_size += blk_prev.m_size;

                            // Resize the previous block to zero
                            element_block_func::resize_block(*blk_prev.mp_data, 0);
                            m_hdl_event.element_block_released(blk_prev.mp_data);

                            // Release both blocks which are no longer used
                            element_block_func::delete_block(blk->mp_data);
                            element_block_func::delete_block(blk_prev.mp_data);

                            // Get an iterator to previous block
                            typename blocks_type::iterator it = m_blocks.begin() + block_index - 1;
        
                            // So we can use it to remove the two blocks
                            m_blocks.erase(it, it+2);
                        }
                        else
                        {
                            // Be sure to resize the next block to zero to prevent the
                            // transferred cells to be deleted. 
                            blk_prev.m_size += 1 + blk_next->m_size;
                            mdds_mtv_append_value(*blk_prev.mp_data, cell);
                            element_block_func::append_values_from_block(*blk_prev.mp_data, *blk_next->mp_data);
                            element_block_func::resize_block(*blk_next->mp_data, 0);
                            m_hdl_event.element_block_released(blk_next->mp_data);
                            element_block_func::delete_block(blk->mp_data);
                            element_block_func::delete_block(blk_next->mp_data);
                            typename blocks_type::iterator it = m_blocks.begin() + block_index;
                            m_blocks.erase(it, it+2);
                        }
                    }
                    else
                    {
                        // Ignore the next block. Just extend the previous block.
                        delete_element_block(m_blocks[block_index]);
                        m_blocks.erase(m_blocks.begin() + block_index);
                        append_cell_to_block(block_index-1, cell);
                    }
                }
            }
            else
            {
                // Extend the previous block to append the cell.
                assert(blk->m_size > 1);
                blk->m_size -= 1;
                append_cell_to_block(block_index-1, cell);
            }

            return get_iterator(block_index-1, start_row-offset);
        }
        else
        {
            // Cell type is different from the type of the previous block.
            if (blk->m_size == 1)
            {
                if (block_index == m_blocks.size()-1)
                {
                    // There is no more block below.
                    create_new_block_with_new_cell(blk->mp_data, cell);
                }
                else
                {
                    // Check the type of the following non-empty block.
                    assert(block_index < m_blocks.size()-1);
                    block* blk_next = get_next_block_of_type(block_index, cat);
                    if (blk_next)
                    {
                        // Remove this empty block, and prepend the cell to the next block.
                        blk_next->m_size += 1;
                        mdds_mtv_prepend_value(*blk_next->mp_data, cell);
                        delete_element_block(m_blocks[block_index]);
                        m_blocks.erase(m_blocks.begin()+block_index);
                    }
                    else
                    {
                        create_new_block_with_new_cell(blk->mp_data, cell);
                    }
                }
            }
            else
            {
                // Replace the current empty block of size > 1 with a
                // non-empty block of size 1, and insert a new empty block
                // below whose size is one shorter than the current empty
                // block.
                size_type new_block_size = blk->m_size - 1;
                blk->m_size = 1;
                create_new_block_with_new_cell(blk->mp_data, cell);
                m_blocks.emplace(m_blocks.begin()+block_index+1, new_block_size);
            }

            return get_iterator(block_index, start_row);
        }
    }
    else if (pos_in_block == blk->m_size - 1)
    {
        // New cell is at the last cell position.
        assert(blk->m_size > 1);
        if (block_index == m_blocks.size()-1)
        {
            // This is the last block.
            blk->m_size -= 1;
            m_blocks.emplace_back(1);
            blk = &m_blocks.back(); // old pointer is invalid.
            create_new_block_with_new_cell(blk->mp_data, cell);
            iterator it = end();
            --it;
            return it;
        }
        else
        {
            // A non-empty block exists below.
            element_category_type cat = mdds_mtv_get_element_type(cell);
            block* blk_next = get_next_block_of_type(block_index, cat);
            if (blk_next)
            {
                // Shrink this empty block and extend the next block.
                blk->m_size -= 1;
                blk_next->m_size += 1;
                mdds_mtv_prepend_value(*blk_next->mp_data, cell);
            }
            else
            {
                // Just insert this new cell.
                blk->m_size -= 1;
                m_blocks.emplace(m_blocks.begin()+block_index+1, 1);
                blk = &m_blocks[block_index]; // old pointer is invalid.
                block& blk2 = m_blocks[block_index+1];
                create_new_block_with_new_cell(blk2.mp_data, cell);
            }

            size_type offset = blk->m_size;
            return get_iterator(block_index+1, start_row+offset);
        }
    }

    // New cell is somewhere in the middle of an empty block.
    return set_cell_to_middle_of_block(start_row, block_index, pos_in_block, cell);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set_cell_to_block_of_size_one(
    size_type start_row, size_type block_index, const _T& cell)
{
    block* blk = &m_blocks[block_index];
    assert(blk->m_size == 1);
    assert(blk->mp_data);
    element_category_type cat = mdds_mtv_get_element_type(cell);
    assert(mdds::mtv::get_block_type(*blk->mp_data) != cat);

    if (block_index == 0)
    {
        // This is the topmost block of size 1.
        if (block_index == m_blocks.size()-1)
        {
            // This is the only block.
            create_new_block_with_new_cell(blk->mp_data, cell);
            return begin();
        }

        // There is an existing block below.
        block* blk_next = get_next_block_of_type(block_index, cat);
        if (!blk_next)
        {
            // Next block is empty or of different type.
            create_new_block_with_new_cell(blk->mp_data, cell);
            return begin();
        }

        // Delete the current block, and prepend the cell to the next block.
        blk_next->m_size += 1;
        mdds_mtv_prepend_value(*blk_next->mp_data, cell);
        delete_element_block(*blk);
        m_blocks.erase(m_blocks.begin()+block_index);
        return begin();
    }

    assert(block_index > 0);

    if (block_index == m_blocks.size()-1)
    {
        // This is the last block, and a block exists above.
        block* blk_prev = &m_blocks[block_index-1];
        if (!blk_prev->mp_data || mdds::mtv::get_block_type(*blk_prev->mp_data) != cat)
        {
            // Previous block is empty. Replace the current block with a new one.
            create_new_block_with_new_cell(blk->mp_data, cell);
        }
        else
        {
            // Append the cell to the previos block, and remove the
            // current block.
            mdds_mtv_append_value(*blk_prev->mp_data, cell);
            blk_prev->m_size += 1;
            delete_element_block(*blk);
            m_blocks.erase(m_blocks.begin()+block_index);
        }

        iterator itr = end();
        --itr;
        return itr;
    }

    // Remove the current block, and check if the cell can be append
    // to the previous block, or prepended to the following block.
    // Also check if the blocks above and below need to be combined.

    block* blk_prev = &m_blocks[block_index-1];
    block* blk_next = &m_blocks[block_index+1];
    if (!blk_prev->mp_data)
    {
        // Previous block is empty.
        if (!blk_next->mp_data)
        {
            // Next block is empty too.
            create_new_block_with_new_cell(blk->mp_data, cell);
            return get_iterator(block_index, start_row);
        }

        // Previous block is empty, but the next block is not.
        element_category_type blk_cat_next = mdds::mtv::get_block_type(*blk_next->mp_data);
        if (blk_cat_next == cat)
        {
            // Delete the current block, and prepend the new cell to the next block.
            delete_element_block(*blk);
            m_blocks.erase(m_blocks.begin()+block_index);
            blk = &m_blocks[block_index];
            blk->m_size += 1;
            mdds_mtv_prepend_value(*blk->mp_data, cell);
            return get_iterator(block_index, start_row);
        }

        assert(blk_cat_next != cat);
        create_new_block_with_new_cell(blk->mp_data, cell);
        return get_iterator(block_index, start_row);
    }

    if (!blk_next->mp_data)
    {
        // Next block is empty.
        assert(blk_prev->mp_data);
        element_category_type blk_cat_prev = mdds::mtv::get_block_type(*blk_prev->mp_data);
        if (blk_cat_prev == cat)
        {
            // Append to the previous block.
            size_type offset = blk_prev->m_size;
            blk_prev->m_size += 1;
            mdds_mtv_append_value(*blk_prev->mp_data, cell);
            delete_element_block(*blk);
            m_blocks.erase(m_blocks.begin()+block_index);
            return get_iterator(block_index-1, start_row-offset);
        }

        // Just overwrite the current block.
        create_new_block_with_new_cell(blk->mp_data, cell);
        return get_iterator(block_index, start_row);
    }

    assert(blk_prev && blk_prev->mp_data);
    assert(blk_next && blk_next->mp_data);
    element_category_type blk_cat_prev = mdds::mtv::get_block_type(*blk_prev->mp_data);
    element_category_type blk_cat_next = mdds::mtv::get_block_type(*blk_next->mp_data);

    if (blk_cat_prev == blk_cat_next)
    {
        if (blk_cat_prev == cat)
        {
            // Merge the previous block with the cell being inserted and
            // the next block.  Resize the next block to zero to prevent
            // deletion of mananged cells on block deletion.
            size_type offset = blk_prev->m_size;
            blk_prev->m_size += 1 + blk_next->m_size;
            mdds_mtv_append_value(*blk_prev->mp_data, cell);
            element_block_func::append_values_from_block(*blk_prev->mp_data, *blk_next->mp_data);
            element_block_func::resize_block(*blk_next->mp_data, 0);

            // Delete the current and next blocks.
            delete_element_block(*blk);
            delete_element_block(*blk_next);
            typename blocks_type::iterator it = m_blocks.begin() + block_index;
            typename blocks_type::iterator it_last = it + 2;
            m_blocks.erase(it, it_last);
            return get_iterator(block_index-1, start_row-offset);
        }

        // Just overwrite the current block.
        create_new_block_with_new_cell(blk->mp_data, cell);
        return get_iterator(block_index, start_row);
    }

    assert(blk_cat_prev != blk_cat_next);

    if (blk_cat_prev == cat)
    {
        // Append to the previous block.
        size_type offset = blk_prev->m_size;
        blk_prev->m_size += 1;
        mdds_mtv_append_value(*blk_prev->mp_data, cell);
        delete_element_block(*blk);
        m_blocks.erase(m_blocks.begin()+block_index);
        return get_iterator(block_index-1, start_row-offset);
    }

    if (blk_cat_next == cat)
    {
        // Prepend to the next block.
        blk_next->m_size += 1;
        mdds_mtv_prepend_value(*blk_next->mp_data, cell);
        delete_element_block(*blk);
        m_blocks.erase(m_blocks.begin()+block_index);
        return get_iterator(block_index, start_row);
    }

    // Just overwrite the current block.
    create_new_block_with_new_cell(blk->mp_data, cell);
    return get_iterator(block_index, start_row);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
void multi_type_vector<_CellBlockFunc, _EventFunc>::set_cell_to_top_of_data_block(size_type block_index, const _T& cell)
{
    block& blk = m_blocks[block_index];
    blk.m_size -= 1;
    if (blk.mp_data)
    {
        element_block_func::overwrite_values(*blk.mp_data, 0, 1);
        element_block_func::erase(*blk.mp_data, 0);
    }
    m_blocks.emplace(m_blocks.begin()+block_index, 1);
    create_new_block_with_new_cell(m_blocks[block_index].mp_data, cell);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
void multi_type_vector<_CellBlockFunc, _EventFunc>::set_cell_to_bottom_of_data_block(size_type block_index, const _T& cell)
{
    assert(block_index < m_blocks.size());
    block& blk = m_blocks[block_index];
    if (blk.mp_data)
    {
        element_block_func::overwrite_values(*blk.mp_data, blk.m_size-1, 1);
        element_block_func::erase(*blk.mp_data, blk.m_size-1);
    }
    blk.m_size -= 1;
    m_blocks.emplace(m_blocks.begin()+block_index+1, 1);
    create_new_block_with_new_cell(m_blocks[block_index+1].mp_data, cell);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
void multi_type_vector<_CellBlockFunc, _EventFunc>::get(size_type pos, _T& value) const
{
    size_type start_row = 0;
    size_type block_index = 0;
    if (!get_block_position(pos, start_row, block_index))
        detail::throw_block_position_not_found("multi_type_vector::get", __LINE__, pos, block_size(), size());

    const block* blk = &m_blocks[block_index];
    assert(blk);

    if (!blk->mp_data)
    {
        // empty cell block.
        mdds_mtv_get_empty_value(value);
        return;
    }

    assert(pos >= start_row);
    assert(blk->mp_data); // data for non-empty blocks should never be nullptr.
    size_type idx = pos - start_row;
    mdds_mtv_get_value(*blk->mp_data, idx, value);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
_T multi_type_vector<_CellBlockFunc, _EventFunc>::get(size_type pos) const
{
    _T cell;
    get(pos, cell);
    return cell;
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
_T multi_type_vector<_CellBlockFunc, _EventFunc>::release(size_type pos)
{
    size_type start_pos = 0;
    size_type block_index = 0;
    if (!get_block_position(pos, start_pos, block_index))
        detail::throw_block_position_not_found("multi_type_vector::release", __LINE__, pos, block_size(), size());

    _T value;
    release_impl(pos, start_pos, block_index, value);
    return value;
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::release(size_type pos, _T& value)
{
    size_type start_pos = 0;
    size_type block_index = 0;
    if (!get_block_position(pos, start_pos, block_index))
        detail::throw_block_position_not_found("multi_type_vector::release", __LINE__, pos, block_size(), size());

    return release_impl(pos, start_pos, block_index, value);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::release(const iterator& pos_hint, size_type pos, _T& value)
{
    size_type start_pos = 0;
    size_type block_index = 0;
    get_block_position(pos_hint, pos, start_pos, block_index);

    return release_impl(pos, start_pos, block_index, value);
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::release()
{
    typename blocks_type::iterator it = m_blocks.begin(), it_end = m_blocks.end();
    for (; it != it_end; ++it)
    {
        block* blk = &(*it);
        if (blk->mp_data)
        {
            element_block_func::resize_block(*blk->mp_data, 0);
            m_hdl_event.element_block_released(blk->mp_data);
            element_block_func::delete_block(blk->mp_data);
        }
    }

    m_blocks.clear();
    m_cur_size = 0;
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::release_range(size_type start_pos, size_type end_pos)
{
    size_type start_pos_in_block1 = 0;
    size_type block_index1 = 0;
    if (!get_block_position(start_pos, start_pos_in_block1, block_index1))
        detail::throw_block_position_not_found("multi_type_vector::release_range", __LINE__, start_pos, block_size(), size());

    return set_empty_impl(start_pos, end_pos, start_pos_in_block1, block_index1, false);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::release_range(
    const iterator& pos_hint, size_type start_pos, size_type end_pos)
{
    size_type start_pos_in_block1 = 0;
    size_type block_index1 = 0;
    get_block_position(pos_hint, start_pos, start_pos_in_block1, block_index1);
    return set_empty_impl(start_pos, end_pos, start_pos_in_block1, block_index1, false);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::position_type
multi_type_vector<_CellBlockFunc, _EventFunc>::position(size_type pos)
{
    size_type start_pos = 0;
    size_type block_index = 0;
    if (!get_block_position(pos, start_pos, block_index))
        detail::throw_block_position_not_found("multi_type_vector::position", __LINE__, pos, block_size(), size());

    iterator it = get_iterator(block_index, start_pos);
    return position_type(it, pos - start_pos);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::position_type
multi_type_vector<_CellBlockFunc, _EventFunc>::position(const iterator& pos_hint, size_type pos)
{
    size_type start_pos = 0;
    size_type block_index = 0;
    get_block_position(pos_hint, pos, start_pos, block_index);

    iterator it = get_iterator(block_index, start_pos);
    return position_type(it, pos - start_pos);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::const_position_type
multi_type_vector<_CellBlockFunc, _EventFunc>::position(size_type pos) const
{
    size_type start_row = 0;
    size_type block_index = 0;
    if (!get_block_position(pos, start_row, block_index))
        detail::throw_block_position_not_found("multi_type_vector::position", __LINE__, pos, block_size(), size());

    typename blocks_type::const_iterator block_pos = m_blocks.begin();
    std::advance(block_pos, block_index);
    const_iterator it = const_iterator(block_pos, m_blocks.end(), start_row, block_index);
    return const_position_type(it, pos - start_row);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::const_position_type
multi_type_vector<_CellBlockFunc, _EventFunc>::position(const const_iterator& pos_hint, size_type pos) const
{
    size_type start_pos = 0;
    size_type block_index = 0;
    get_block_position(pos_hint, pos, start_pos, block_index);

    const_iterator it = get_const_iterator(block_index, start_pos);
    return const_position_type(it, pos - start_pos);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::transfer(
    size_type start_pos, size_type end_pos, multi_type_vector& dest, size_type dest_pos)
{
    if (&dest == this)
        throw invalid_arg_error("You cannot transfer between the same container.");

    size_type start_pos_in_block1 = 0;
    size_type block_index1 = 0;
    if (!get_block_position(start_pos, start_pos_in_block1, block_index1))
        detail::throw_block_position_not_found("multi_type_vector::transfer", __LINE__, start_pos, block_size(), size());

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    std::ostringstream os_prev_block;
    os_prev_block << "source:" << endl;
    dump_blocks(os_prev_block);
    os_prev_block << "destination:" << endl;
    dest.dump_blocks(os_prev_block);
#endif

    iterator ret = transfer_impl(start_pos, end_pos, start_pos_in_block1, block_index1, dest, dest_pos);

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    if (!check_block_integrity() || !dest.check_block_integrity())
    {
        cerr << "block integrity check failed in transfer (start_pos=" << start_pos
            << ",end_pos=" << end_pos << ",dest_pos=" << dest_pos << ")" << endl;
        cerr << "previous block state:" << endl;
        cerr << os_prev_block.str();
        abort();
    }
#endif

    return ret;
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::transfer(
    const iterator& pos_hint, size_type start_pos, size_type end_pos,
    multi_type_vector& dest, size_type dest_pos)
{
    size_type start_pos_in_block1 = 0;
    size_type block_index1 = 0;
    get_block_position(pos_hint, start_pos, start_pos_in_block1, block_index1);

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    std::ostringstream os_prev_block;
    os_prev_block << "source:" << endl;
    dump_blocks(os_prev_block);
    os_prev_block << "destination:" << endl;
    dest.dump_blocks(os_prev_block);
#endif

    iterator ret = transfer_impl(start_pos, end_pos, start_pos_in_block1, block_index1, dest, dest_pos);

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    if (!check_block_integrity() || !dest.check_block_integrity())
    {
        cerr << "block integrity check failed in transfer (start_pos=" << start_pos
            << ",end_pos=" << end_pos << ",dest_pos=" << dest_pos << ")" << endl;
        cerr << "previous block state:" << endl;
        cerr << os_prev_block.str();
        abort();
    }
#endif

    return ret;
}

template<typename _CellBlockFunc, typename _EventFunc>
mtv::element_t multi_type_vector<_CellBlockFunc, _EventFunc>::get_type(size_type pos) const
{
    size_type start_row = 0;
    size_type block_index = 0;
    if (!get_block_position(pos, start_row, block_index))
        detail::throw_block_position_not_found("multi_type_vector::get_type", __LINE__, pos, block_size(), size());

    const block* blk = &m_blocks[block_index];
    if (!blk->mp_data)
        return mtv::element_type_empty;

    return mtv::get_block_type(*blk->mp_data);
}

template<typename _CellBlockFunc, typename _EventFunc>
bool multi_type_vector<_CellBlockFunc, _EventFunc>::is_empty(size_type pos) const
{
    size_type start_row = 0;
    size_type block_index = 0;
    if (!get_block_position(pos, start_row, block_index))
        detail::throw_block_position_not_found("multi_type_vector::is_empty", __LINE__, pos, block_size(), size());

    return m_blocks[block_index].mp_data == nullptr;
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set_empty(size_type start_pos, size_type end_pos)
{
    size_type start_pos_in_block1 = 0;
    size_type block_index1 = 0;
    if (!get_block_position(start_pos, start_pos_in_block1, block_index1))
        detail::throw_block_position_not_found("multi_type_vector::set_empty", __LINE__, start_pos, block_size(), size());

    return set_empty_impl(start_pos, end_pos, start_pos_in_block1, block_index1, true);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set_empty(const iterator& pos_hint, size_type start_pos, size_type end_pos)
{
    size_type start_pos_in_block1 = 0;
    size_type block_index1 = 0;
    get_block_position(pos_hint, start_pos, start_pos_in_block1, block_index1);
    return set_empty_impl(start_pos, end_pos, start_pos_in_block1, block_index1, true);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::transfer_impl(
    size_type start_pos, size_type end_pos, size_type start_pos_in_block1, size_type block_index1,
    multi_type_vector& dest, size_type dest_pos)
{
    if (start_pos > end_pos)
    {
        std::ostringstream os;
        os << "multi_type_vector::transfer_impl: start position is larger than the end position. (start=";
        os << start_pos << ", end=" << end_pos << ")";
        throw std::out_of_range(os.str());
    }

    size_type start_pos_in_block2 = start_pos_in_block1;
    size_type block_index2 = block_index1;
    if (!get_block_position(end_pos, start_pos_in_block2, block_index2))
        detail::throw_block_position_not_found("multi_type_vector::transfer_impl", __LINE__, end_pos, block_size(), size());

    size_type len = end_pos - start_pos + 1;
    size_type last_dest_pos = dest_pos + len - 1;

    // Make sure the destination container is large enough.
    if (last_dest_pos >= dest.size())
        throw std::out_of_range("Destination vector is too small for the elements being transferred.");

    if (block_index1 == block_index2)
    {
        // All elements are in the same block.
        return transfer_single_block(start_pos, end_pos, start_pos_in_block1, block_index1, dest, dest_pos);
    }

    return transfer_multi_blocks(
        start_pos, end_pos, start_pos_in_block1, block_index1, start_pos_in_block2, block_index2, dest, dest_pos);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::transfer_single_block(
    size_type start_pos, size_type end_pos, size_type start_pos_in_block1, size_type block_index1,
    multi_type_vector& dest, size_type dest_pos)
{
    size_type len = end_pos - start_pos + 1;
    size_type last_dest_pos = dest_pos + len - 1;

    // All elements are in the same block.
    block* blk = &m_blocks[block_index1];

    // Empty the region in the destination container where the elements
    // are to be transferred to. This ensures that the destination region
    // consists of a single block.
    iterator it_dest_blk = dest.set_empty(dest_pos, last_dest_pos);

    if (!blk->mp_data)
        return get_iterator(block_index1, start_pos_in_block1);

    element_category_type cat = get_block_type(*blk->mp_data);

    size_type dest_block_index = it_dest_blk->__private_data.block_index;
    block* blk_dest = &dest.m_blocks[dest_block_index];

    size_type dest_pos_in_block = dest_pos - it_dest_blk->position;
    if (dest_pos_in_block == 0)
    {
        // Copy to the top part of destination block.

        assert(!blk_dest->mp_data); // should be already emptied.

        if (len < blk_dest->m_size)
        {
            // Shrink the existing block and insert a new block before it.
            assert(len < blk_dest->m_size);
            blk_dest->m_size -= len;
            dest.m_blocks.emplace(dest.m_blocks.begin()+dest_block_index, len);
            blk_dest = &dest.m_blocks[dest_block_index]; // The old pointer is invalid.
        }
    }
    else if (dest_pos_in_block + len - 1 == it_dest_blk->size - 1)
    {
        // Copy to the bottom part of destination block.

        // Insert a new block below current, and shrink the current block.
        dest.m_blocks.emplace(dest.m_blocks.begin()+dest_block_index+1, len);
        dest.m_blocks[dest_block_index].m_size -= len;
        blk_dest = &dest.m_blocks[dest_block_index+1];
        ++dest_block_index; // Must point to the new copied block.
    }
    else
    {
        // Copy to the middle of destination block.

        // Insert two new blocks below current.
        size_type blk2_size = blk_dest->m_size - dest_pos_in_block - len;
        dest.m_blocks.insert(dest.m_blocks.begin()+dest_block_index+1, 2u, block());
        dest.m_blocks[dest_block_index].m_size = dest_pos_in_block;
        dest.m_blocks[dest_block_index+1].m_size = len;
        dest.m_blocks[dest_block_index+2].m_size = blk2_size;

        blk_dest = &dest.m_blocks[dest_block_index+1];

        ++dest_block_index; // Must point to the new copied block.
    }

    assert(blk_dest->m_size == len);
    size_type offset = start_pos - start_pos_in_block1;
    if (offset == 0 && len == blk->m_size)
    {
        // Just move the whole data array.
        blk_dest->mp_data = blk->mp_data;
        dest.m_hdl_event.element_block_acquired(blk_dest->mp_data);

        m_hdl_event.element_block_released(blk->mp_data);
        blk->mp_data = nullptr;

        dest.merge_with_adjacent_blocks(dest_block_index);
        size_type start_pos_offset = merge_with_adjacent_blocks(block_index1);
        if (start_pos_offset)
        {
            // Merged with the previous block. Adjust the return block position.
            --block_index1;
            start_pos_in_block1 -= start_pos_offset;
        }
        return get_iterator(block_index1, start_pos_in_block1);
    }

    blk_dest->mp_data = element_block_func::create_new_block(cat, 0);
    assert(blk_dest->mp_data);
    dest.m_hdl_event.element_block_acquired(blk_dest->mp_data);

    // Shallow-copy the elements to the destination block.
    element_block_func::assign_values_from_block(*blk_dest->mp_data, *blk->mp_data, offset, len);
    dest.merge_with_adjacent_blocks(dest_block_index);

    // Set the source range empty without overwriting the elements.
    return set_empty_in_single_block(start_pos, end_pos, block_index1, start_pos_in_block1, false);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::transfer_multi_blocks(
    size_type start_pos, size_type end_pos, size_type start_pos_in_block1, size_type block_index1,
    size_type start_pos_in_block2, size_type block_index2,
    multi_type_vector& dest, size_type dest_pos)
{
    assert(block_index1 < block_index2);

    size_type len = end_pos - start_pos + 1;
    size_type last_dest_pos = dest_pos + len - 1;

    // Empty the region in the destination container where the elements
    // are to be transferred to. This ensures that the destination region
    // consists of a single block.
    iterator it_dest_blk = dest.set_empty(dest_pos, last_dest_pos);

    size_type dest_block_index = it_dest_blk->__private_data.block_index;
    size_type dest_pos_in_block = dest_pos - it_dest_blk->position;
    block* blk_dest = &dest.m_blocks[dest_block_index];
    assert(!blk_dest->mp_data); // should be already emptied.

    size_type block_len = block_index2 - block_index1 + 1;

    // Create slots for new blocks in the destination.

    size_type dest_block_index1 = dest_block_index;
    if (dest_pos_in_block == 0)
    {
        // Copy to the top part of destination block.
        if (len < blk_dest->m_size)
        {
            // Shrink the existing block and insert slots for new blocks before it.
            blk_dest->m_size -= len;
            dest.m_blocks.insert(dest.m_blocks.begin()+dest_block_index, block_len, block());
            blk_dest = &dest.m_blocks[dest_block_index+block_len];
        }
        else
        {
            // Destination block is exactly of the length of the elements being transferred.
            dest.delete_element_block(*blk_dest);
            blk_dest->m_size = 0;
            if (block_len > 1)
            {
                dest.m_blocks.insert(dest.m_blocks.begin()+dest_block_index, block_len-1, block());
                blk_dest = &dest.m_blocks[dest_block_index+block_len-1];
            }
        }
    }
    else if (dest_pos_in_block + len - 1 == it_dest_blk->size - 1)
    {
        // Copy to the bottom part of destination block. Insert slots for new
        // blocks below current, and shrink the current block.
        dest.m_blocks.insert(dest.m_blocks.begin()+dest_block_index+1, block_len, block());
        blk_dest = &dest.m_blocks[dest_block_index];
        blk_dest->m_size -= len;

        ++dest_block_index1;
    }
    else
    {
        // Copy to the middle of destination block. Insert slots for new
        // blocks (plus one for the bottom empty block) below current.
        size_type blk2_size = blk_dest->m_size - dest_pos_in_block - len;
        dest.m_blocks.insert(dest.m_blocks.begin()+dest_block_index+1, block_len+1, block());
        blk_dest = &dest.m_blocks[dest_block_index];
        assert(dest.m_blocks.size() > dest_block_index+block_len+1);
        dest.m_blocks[dest_block_index+block_len+1].m_size = blk2_size;
        blk_dest->m_size = dest_pos_in_block;

        ++dest_block_index1;
    }

    size_type del_index1 = block_index1, del_index2 = block_index2;
    size_type ret_block_index = block_index1, ret_start_pos = start_pos_in_block1;

    // Now that the new slots have been created, start transferring the blocks.

    // Transfer the first block.
    size_type offset = start_pos - start_pos_in_block1;
    if (offset)
    {
        // Transfer the lower part of the first block.
        block* blk = &m_blocks[block_index1];
        assert(dest.m_blocks[dest_block_index1].m_size == 0);
        dest.m_blocks[dest_block_index1].m_size = blk->m_size - offset;
        if (blk->mp_data)
        {
            element_category_type cat = mtv::get_block_type(*blk->mp_data);
            blk_dest = &dest.m_blocks[dest_block_index1];
            blk_dest->mp_data = element_block_func::create_new_block(cat, 0);
            assert(blk_dest->mp_data);
            dest.m_hdl_event.element_block_acquired(blk_dest->mp_data);

            // Shallow-copy the elements to the destination block, and shrink
            // the source block to remove the transferred elements.
            element_block_func::assign_values_from_block(*blk_dest->mp_data, *blk->mp_data, offset, blk->m_size-offset);
            element_block_func::resize_block(*blk->mp_data, offset);
        }

        blk->m_size = offset;
        ++del_index1; // Retain this block.

        // Move the return block position to the next block.
        ++ret_block_index;
        ret_start_pos += blk->m_size;
    }
    else
    {
        // Just move the whole block over.
        block& blk = m_blocks[block_index1];
        dest.m_blocks[dest_block_index1] = blk; // copied.
        if (blk.mp_data)
        {
            dest.m_hdl_event.element_block_acquired(blk.mp_data);
            m_hdl_event.element_block_released(blk.mp_data);
            blk.mp_data = nullptr;
        }
        blk.m_size = 0;
    }

    if (block_len > 2)
    {
        // Transfer all blocks in between.
        for (size_type i = 0; i < block_len - 2; ++i)
        {
            size_type src_block_pos = block_index1 + 1 + i;
            size_type dest_block_pos = dest_block_index1 + 1 + i;
            assert(dest.m_blocks[dest_block_pos].m_size == 0);
            block& blk = m_blocks[src_block_pos];
            dest.m_blocks[dest_block_pos] = blk; // copied.
            if (blk.mp_data)
            {
                dest.m_hdl_event.element_block_acquired(blk.mp_data);
                m_hdl_event.element_block_released(blk.mp_data);
                blk.mp_data = nullptr;
            }
            m_blocks[src_block_pos].m_size = 0;
        }
    }

    // Transfer the last block.
    if (block_len > 1)
    {
        size_type size_to_trans = end_pos - start_pos_in_block2 + 1;
        size_type dest_block_pos = dest_block_index1 + block_len - 1;
        assert(dest.m_blocks[dest_block_pos].m_size == 0);

        block& blk = m_blocks[block_index2];
        if (size_to_trans < blk.m_size)
        {
            // Transfer the upper part of this block.
            dest.m_blocks[dest_block_pos].m_size = size_to_trans;
            blk_dest = &dest.m_blocks[dest_block_pos];
            if (blk.mp_data)
            {
                element_category_type cat = mtv::get_block_type(*blk.mp_data);
                blk_dest->mp_data = element_block_func::create_new_block(cat, 0);
                dest.m_hdl_event.element_block_acquired(blk_dest->mp_data);

                element_block_func::assign_values_from_block(*blk_dest->mp_data, *blk.mp_data, 0, size_to_trans);
                element_block_func::erase(*blk.mp_data, 0, size_to_trans);
            }
            blk.m_size -= size_to_trans;
            --del_index2; // Retain this block.
        }
        else
        {
            // Just move the whole block over.
            dest.m_blocks[dest_block_pos] = blk;
            if (blk.mp_data)
            {
                dest.m_hdl_event.element_block_acquired(blk.mp_data);
                m_hdl_event.element_block_released(blk.mp_data);
                blk.mp_data = nullptr;
            }
            m_blocks[block_index2].m_size = 0;
        }
    }

    // Now that all the elements have been transferred, check the bordering
    // blocks in the destination and merge them as needed.
    if (block_len > 1)
        dest.merge_with_adjacent_blocks(dest_block_index1+block_len-1);
    dest.merge_with_adjacent_blocks(dest_block_index1);

    // Delete all transferred blocks, and replace it with one empty block.
    if (del_index2 < del_index1)
    {
        // No blocks will be deleted.  See if we can just extend one of the
        // neighboring empty blocks.

        block& blk1 = m_blocks[block_index1];
        block& blk2 = m_blocks[block_index2];

        if (!blk1.mp_data)
        {
            assert(blk2.mp_data);

            // Block 1 is empty. Extend this block.
            blk1.m_size += len;
            return get_iterator(block_index1, start_pos_in_block1);
        }

        if (!blk2.mp_data)
        {
            assert(blk1.mp_data);

            // Block 2 is empty. Extend this block.
            blk2.m_size += len;
            return get_iterator(block_index2, start_pos);
        }

        // Neither block1 nor block2 are empty. Just insert a new empty block
        // between them. After the insertion, the old block2 position becomes
        // the position of the inserted block.
        m_blocks.emplace(m_blocks.begin()+block_index2, len);
        // No need to adjust local index vars
        return get_iterator(block_index2, start_pos);
    }

    if (del_index1 > 0 && !m_blocks[del_index1-1].mp_data)
    {
        // The block before the first block to be deleted is empty.  Simply
        // extend that block to cover the deleted block segment.
        block& blk_prev = m_blocks[del_index1-1];

        // This previous empty block will be returned.  Adjust the return block position.
        --ret_block_index;
        ret_start_pos -= blk_prev.m_size;

        // Extend the previous block.
        blk_prev.m_size += len;
    }
    else
    {
        // Block before is not empty (or doesn't exist).  Keep the first slot,
        // and erase the rest.
        m_blocks[del_index1].m_size = len; // Insert an empty
        ++del_index1;
    }

    if (del_index2 >= del_index1)
    {
        typename blocks_type::iterator it_blk = m_blocks.begin();
        typename blocks_type::iterator it_blk_end = m_blocks.begin();
        std::advance(it_blk, del_index1);
        std::advance(it_blk_end, del_index2+1);

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
        typename blocks_type::iterator it_test = it_blk;
        for (; it_test != it_blk_end; ++it_test)
        {
            // All slots to be erased should have zero size
            assert(it_test->m_size == 0);
        }
#endif
        m_blocks.erase(it_blk, it_blk_end);
    }

    size_type start_pos_offset = merge_with_adjacent_blocks(ret_block_index);
    if (start_pos_offset)
    {
        // Merged with the previous block. Adjust the return block position.
        --ret_block_index;
        ret_start_pos -= start_pos_offset;
    }

    return get_iterator(ret_block_index, ret_start_pos);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set_empty_impl(
    size_type start_pos, size_type end_pos, size_type start_pos_in_block1, size_type block_index1,
    bool overwrite)
{
    if (start_pos > end_pos)
        throw std::out_of_range("Start row is larger than the end row.");

    size_type start_pos_in_block2 = start_pos_in_block1;
    size_type block_index2 = block_index1;
    if (!get_block_position(end_pos, start_pos_in_block2, block_index2))
        detail::throw_block_position_not_found("multi_type_vector::set_empty_impl", __LINE__, end_pos, block_size(), size());

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    std::ostringstream os_prev_block;
    dump_blocks(os_prev_block);
#endif

    iterator ret_it;
    if (block_index1 == block_index2)
        ret_it = set_empty_in_single_block(start_pos, end_pos, block_index1, start_pos_in_block1, overwrite);
    else
        ret_it = set_empty_in_multi_blocks(
            start_pos, end_pos, block_index1, start_pos_in_block1, block_index2, start_pos_in_block2, overwrite);

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    if (!check_block_integrity())
    {
        cerr << "block integrity check failed in set_empty (" << start_pos << "-" << end_pos << ")" << endl;
        cerr << "previous block state:" << endl;
        cerr << os_prev_block.str();
        abort();
    }
#endif
    return ret_it;
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::swap_impl(
    multi_type_vector& other, size_type start_pos, size_type end_pos, size_type other_pos,
    size_type start_pos_in_block1, size_type block_index1, size_type start_pos_in_block2, size_type block_index2,
    size_type start_pos_in_dblock1, size_type dblock_index1, size_type start_pos_in_dblock2, size_type dblock_index2)
{
    if (block_index1 == block_index2)
    {
        // Source range is in a single block.
        if (dblock_index1 == dblock_index2)
        {
            // Destination range is also in a single block.
            swap_single_block(
                other, start_pos, end_pos, other_pos, start_pos_in_block1, block_index1,
                start_pos_in_dblock1, dblock_index1);
        }
        else
        {
            // Source is single-, and destination is multi-blocks.
            swap_single_to_multi_blocks(
                other, start_pos, end_pos, other_pos,
                start_pos_in_block1, block_index1,
                start_pos_in_dblock1, dblock_index1, start_pos_in_dblock2, dblock_index2);
        }
    }
    else if (dblock_index1 == dblock_index2)
    {
        // Destination range is over a single block. Switch source and destination.
        size_type len = end_pos - start_pos + 1;
        other.swap_single_to_multi_blocks(
            *this, other_pos, other_pos+len-1, start_pos,
            start_pos_in_dblock1, dblock_index1,
            start_pos_in_block1, block_index1, start_pos_in_block2, block_index2);
    }
    else
    {
        // Both source and destinations are multi-block.
        swap_multi_to_multi_blocks(
            other, start_pos, end_pos, other_pos, start_pos_in_block1, block_index1,
            start_pos_in_block2, block_index2, start_pos_in_dblock1, dblock_index1,
            start_pos_in_dblock2, dblock_index2);
    }
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::swap_single_block(
    multi_type_vector& other, size_type start_pos, size_type end_pos, size_type other_pos,
    size_type start_pos_in_block, size_type block_index, size_type start_pos_in_other_block, size_type other_block_index)
{
    block* blk_src = &m_blocks[block_index];
    block* blk_dst = &other.m_blocks[other_block_index];
    element_category_type cat_src = mtv::element_type_empty;
    element_category_type cat_dst = mtv::element_type_empty;

    if (blk_src->mp_data)
        cat_src = mtv::get_block_type(*blk_src->mp_data);
    if (blk_dst->mp_data)
        cat_dst = mtv::get_block_type(*blk_dst->mp_data);

    size_t other_end_pos = other_pos + end_pos - start_pos;
    size_t len = end_pos - start_pos + 1; // length of elements to swap.
    size_type src_offset = start_pos - start_pos_in_block;
    size_type dst_offset = other_pos - start_pos_in_other_block;

    // length of the tail that will not be swapped.
    size_type src_tail_len = blk_src->m_size - src_offset - len;

    if (cat_src == cat_dst)
    {
        // Source and destination blocks are of the same type.
        if (cat_src == mtv::element_type_empty)
            // Both are empty blocks. Nothing to swap.
            return;

        element_block_func::swap_values(*blk_src->mp_data, *blk_dst->mp_data, src_offset, dst_offset, len);
        return;
    }

    // Source and destination blocks are of different types.

    if (cat_src == mtv::element_type_empty)
    {
        // Source is empty but destination is not. This is equivalent of transfer.
        other.transfer_single_block(other_pos, other_end_pos, start_pos_in_other_block, other_block_index, *this, start_pos);
        // No update of local index vars needed.
        return;
    }

    if (cat_dst == mtv::element_type_empty)
    {
        // Source is not empty but destination is. Use transfer.
        transfer_single_block(start_pos, end_pos, start_pos_in_block, block_index, other, other_pos);
        // No update of local index vars needed.
        return;
    }

    // Neither the source nor destination blocks are empty, and they are of different types.
    if (src_offset == 0)
    {
        // Source range is at the top of a block.
        if (src_tail_len == 0)
        {
            // the whole block needs to be replaced.
            std::unique_ptr<element_block_type, element_block_deleter> src_data(blk_src->mp_data);
            m_hdl_event.element_block_released(blk_src->mp_data);
            blk_src->mp_data = other.exchange_elements(
                *src_data, src_offset, other_block_index, dst_offset, len);
            m_hdl_event.element_block_acquired(blk_src->mp_data);

            // Release elements in the source block to prevent double-deletion.
            element_block_func::resize_block(*src_data, 0);
            merge_with_adjacent_blocks(block_index);
            return;
        }

        // Get the new elements from the other container.
        std::unique_ptr<element_block_type, element_block_deleter> dst_data(
            other.exchange_elements(*blk_src->mp_data, src_offset, other_block_index, dst_offset, len));

        // Shrink the current block by erasing the top part.
        element_block_func::erase(*blk_src->mp_data, 0, len);
        blk_src->m_size -= len;

        block* blk_prev = get_previous_block_of_type(block_index, cat_dst);
        if (blk_prev)
        {
            // Append the new elements to the previous block.
            element_block_func::append_values_from_block(*blk_prev->mp_data, *dst_data);
            element_block_func::resize_block(*dst_data, 0); // prevent double-delete.
            blk_prev->m_size += len;
        }
        else
        {
            // Insert a new block to store the new elements.
            m_blocks.emplace(m_blocks.begin()+block_index, len);
            block& blk = m_blocks[block_index];
            blk.mp_data = dst_data.release();
            m_hdl_event.element_block_acquired(blk.mp_data);
        }
        return;
    }

    // Get the new elements from the other container.
    std::unique_ptr<element_block_type, element_block_deleter> dst_data(
        other.exchange_elements(*blk_src->mp_data, src_offset, other_block_index, dst_offset, len));

    if (src_tail_len == 0)
    {
        // Source range is at the bottom of a block.

        // Shrink the current block.
        element_block_func::resize_block(*blk_src->mp_data, src_offset);
        blk_src->m_size = src_offset;

        block* blk_next = get_next_block_of_type(block_index, cat_dst);
        if (blk_next)
        {
            // Merge with the next block.
            element_block_func::prepend_values_from_block(*blk_next->mp_data, *dst_data, 0, len);
            element_block_func::resize_block(*dst_data, 0); // prevent double-delete.
            blk_next->m_size += len;
        }
        else
        {
            m_blocks.emplace(m_blocks.begin()+block_index+1, len);
            block& blk = m_blocks[block_index+1];
            blk.mp_data = dst_data.release();
            m_hdl_event.element_block_acquired(blk.mp_data);
        }
        return;
    }

    // Source range is in the middle of a block.
    assert(src_offset && src_tail_len);
    block& blk = set_new_block_to_middle(block_index, src_offset, len, false);
    blk.mp_data = dst_data.release();
    m_hdl_event.element_block_acquired(blk.mp_data);
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::swap_single_to_multi_blocks(
    multi_type_vector& other, size_type start_pos, size_type end_pos, size_type other_pos,
    size_type start_pos_in_block, size_type block_index, size_type dst_start_pos_in_block1, size_type dst_block_index1,
    size_type dst_start_pos_in_block2, size_type dst_block_index2)
{
    block* blk_src = &m_blocks[block_index];
    element_category_type cat_src = mtv::element_type_empty;
    if (blk_src->mp_data)
        cat_src = mtv::get_block_type(*blk_src->mp_data);

    size_type len = end_pos - start_pos + 1;

    if (cat_src == mtv::element_type_empty)
    {
        // The source block is empty. Use transfer.
        other.transfer_multi_blocks(
            other_pos, other_pos+len-1,
            dst_start_pos_in_block1, dst_block_index1, dst_start_pos_in_block2, dst_block_index2, *this, start_pos);
        return;
    }

    size_type src_offset = start_pos - start_pos_in_block;
    size_type dst_offset1 = other_pos - dst_start_pos_in_block1;
    size_type dst_offset2 = other_pos + len - 1 - dst_start_pos_in_block2;

    // length of the tail that will not be swapped.
    size_type src_tail_len = blk_src->m_size - src_offset - len;

    // Get the new elements from the other container.
    blocks_type new_blocks;
    other.exchange_elements(
        *blk_src->mp_data, src_offset, dst_block_index1, dst_offset1, dst_block_index2, dst_offset2, len, new_blocks);

    if (new_blocks.empty())
        throw general_error("multi_type_vector::swap_single_to_multi_blocks: failed to exchange elements.");

    if (src_offset == 0)
    {
        // Source range is at the top of a block.

        if (src_tail_len == 0)
        {
            // the whole block needs to be replaced.  Delete the block, but
            // don't delete the managed elements the block contains since they
            // have been transferred over to the destination block.
            element_block_func::resize_block(*blk_src->mp_data, 0);
            delete_element_block(*blk_src);
            m_blocks.erase(m_blocks.begin()+block_index);
        }
        else
        {
            // Shrink the current block by erasing the top part.
            element_block_func::erase(*blk_src->mp_data, 0, len);
            blk_src->m_size -= len;
        }

        insert_blocks_at(block_index, new_blocks);
        merge_with_next_block(block_index+new_blocks.size()-1); // last block inserted.
        if (block_index > 0)
            merge_with_next_block(block_index-1); // block before the first block inserted.

        return;
    }

    if (src_tail_len == 0)
    {
        // Source range is at the bottom of a block.

        // Shrink the current block.
        element_block_func::resize_block(*blk_src->mp_data, src_offset);
        blk_src->m_size = src_offset;
    }
    else
    {
        // Source range is in the middle of a block.
        assert(src_offset && src_tail_len);

        // This creates an empty block at block_index+1.
        set_new_block_to_middle(block_index, src_offset, len, false);
        delete_element_block(m_blocks[block_index+1]);
        m_blocks.erase(m_blocks.begin()+block_index+1);
    }

    insert_blocks_at(block_index+1, new_blocks);
    merge_with_next_block(block_index+new_blocks.size()); // last block inserted.
    merge_with_next_block(block_index); // block before the first block inserted.
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::swap_multi_to_multi_blocks(
    multi_type_vector& other, size_type start_pos, size_type end_pos, size_type other_pos,
    size_type start_pos_in_block1, size_type block_index1, size_type start_pos_in_block2, size_type block_index2,
    size_type start_pos_in_dblock1, size_type dblock_index1, size_type start_pos_in_dblock2, size_type dblock_index2)
{
    assert(block_index1 < block_index2);
    assert(dblock_index1 < dblock_index2);

    size_type len = end_pos - start_pos + 1;
    size_type src_offset1 = start_pos - start_pos_in_block1;
    size_type src_offset2 = end_pos - start_pos_in_block2;
    size_type dst_offset1 = other_pos - start_pos_in_dblock1;
    size_type dst_offset2 = other_pos + len - 1 - start_pos_in_dblock2;

    blocks_to_transfer src_bucket, dst_bucket;
    prepare_blocks_to_transfer(src_bucket, block_index1, src_offset1, block_index2, src_offset2);
    other.prepare_blocks_to_transfer(dst_bucket, dblock_index1, dst_offset1, dblock_index2, dst_offset2);

    m_blocks.insert(
        m_blocks.begin()+src_bucket.insert_index, dst_bucket.blocks.begin(), dst_bucket.blocks.end());

    // Merge the boundary blocks in the source.
    merge_with_next_block(src_bucket.insert_index + dst_bucket.blocks.size()-1);
    if (src_bucket.insert_index > 0)
        merge_with_next_block(src_bucket.insert_index - 1);

    other.m_blocks.insert(
        other.m_blocks.begin()+dst_bucket.insert_index, src_bucket.blocks.begin(), src_bucket.blocks.end());

    // Merge the boundary blocks in the destination.
    other.merge_with_next_block(dst_bucket.insert_index + src_bucket.blocks.size()-1);
    if (dst_bucket.insert_index > 0)
        other.merge_with_next_block(dst_bucket.insert_index-1);
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::insert_blocks_at(
    size_type insert_pos, blocks_type& new_blocks)
{
    std::for_each(new_blocks.begin(), new_blocks.end(),
        [&](block& r)
        {
            if (r.mp_data)
                m_hdl_event.element_block_acquired(r.mp_data);
        }
    );
    m_blocks.insert(m_blocks.begin()+insert_pos, new_blocks.begin(), new_blocks.end());
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::prepare_blocks_to_transfer(
    blocks_to_transfer& bucket, size_type block_index1, size_type offset1, size_type block_index2, size_type offset2)
{
    assert(block_index1 < block_index2);
    assert(offset1 < m_blocks[block_index1].m_size);
    assert(offset2 < m_blocks[block_index2].m_size);

    block block_first;
    block block_last;
    typename blocks_type::iterator it_begin = m_blocks.begin();
    typename blocks_type::iterator it_end = m_blocks.begin();

    std::advance(it_begin, block_index1+1);
    std::advance(it_end, block_index2);
    bucket.insert_index = block_index1+1;

    if (offset1 == 0)
    {
        // The whole first block needs to be swapped.
        --it_begin;
        --bucket.insert_index;
    }
    else
    {
        // Copy the lower part of the block for transfer.
        block* blk = &m_blocks[block_index1];
        size_type blk_size = blk->m_size - offset1;
        block_first.m_size = blk_size;
        if (blk->mp_data)
        {
            block_first.mp_data = element_block_func::create_new_block(mtv::get_block_type(*blk->mp_data), 0);
            element_block_func::assign_values_from_block(*block_first.mp_data, *blk->mp_data, offset1, blk_size);

            // Shrink the existing block.
            element_block_func::resize_block(*blk->mp_data, offset1);
        }

        blk->m_size = offset1;
    }

    block* blk = &m_blocks[block_index2];
    if (offset2 == blk->m_size-1)
    {
        // The whole last block needs to be swapped.
        ++it_end;
    }
    else
    {
        // Copy the upper part of the block for transfer.
        size_type blk_size = offset2 + 1;
        block_last.m_size = blk_size;
        if (blk->mp_data)
        {
            block_last.mp_data = element_block_func::create_new_block(mtv::get_block_type(*blk->mp_data), 0);
            element_block_func::assign_values_from_block(*block_last.mp_data, *blk->mp_data, 0, blk_size);

            // Shrink the existing block.
            element_block_func::erase(*blk->mp_data, 0, blk_size);
        }

        blk->m_size -= blk_size;
    }

    // Copy all blocks into the bucket.
    if (block_first.m_size)
        bucket.blocks.push_back(std::move(block_first));

    std::for_each(it_begin, it_end,
        [&](block& r)
        {
            if (r.mp_data)
                m_hdl_event.element_block_released(r.mp_data);
            bucket.blocks.push_back(r);
        }
    );

    if (block_last.m_size)
        bucket.blocks.push_back(std::move(block_last));

    // Remove the slots for these blocks (but don't delete the blocks).
    m_blocks.erase(it_begin, it_end);
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::erase(size_type start_pos, size_type end_pos)
{
    if (start_pos > end_pos)
        throw std::out_of_range("Start row is larger than the end row.");

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    std::ostringstream os_prev_block;
    dump_blocks(os_prev_block);
#endif

    erase_impl(start_pos, end_pos);

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    if (!check_block_integrity())
    {
        cerr << "block integrity check failed in erase (" << start_pos << "-" << end_pos << ")" << endl;
        cerr << "previous block state:" << endl;
        cerr << os_prev_block.str();
        abort();
    }
#endif
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::erase_impl(size_type start_row, size_type end_row)
{
    assert(start_row <= end_row);

    // Keep the logic similar to set_empty().

    size_type start_row_in_block1 = 0;
    size_type block_pos1 = 0;
    if (!get_block_position(start_row, start_row_in_block1, block_pos1))
        detail::throw_block_position_not_found("multi_type_vector::erase_impl", __LINE__, start_row, block_size(), size());

    size_type start_row_in_block2 = start_row_in_block1;
    size_type block_pos2 = block_pos1;
    if (!get_block_position(end_row, start_row_in_block2, block_pos2))
        detail::throw_block_position_not_found("multi_type_vector::erase_impl", __LINE__, end_row, block_size(), size());

    if (block_pos1 == block_pos2)
    {
        erase_in_single_block(start_row, end_row, block_pos1, start_row_in_block1);
        return;
    }

    assert(block_pos1 < block_pos2);

    // Initially, we set to erase all blocks between the first and the last.
    typename blocks_type::iterator it_erase_begin = m_blocks.begin() + block_pos1 + 1;
    typename blocks_type::iterator it_erase_end   = m_blocks.begin() + block_pos2;

    // First, inspect the first block.
    if (start_row_in_block1 == start_row)
    {
        // Erase the whole block.
        --it_erase_begin;
    }
    else
    {
        // Erase the lower part of the first block.
        block* blk = &m_blocks[block_pos1];
        size_type new_size = start_row - start_row_in_block1;
        if (blk->mp_data)
        {
            // Shrink the data array.
            element_block_func::overwrite_values(*blk->mp_data, new_size, blk->m_size-new_size);
            element_block_func::resize_block(*blk->mp_data, new_size);
        }
        blk->m_size = new_size;
    }

    // Then inspect the last block.
    block* blk = &m_blocks[block_pos2];
    size_type last_row_in_block = start_row_in_block2 + blk->m_size - 1;
    if (last_row_in_block == end_row)
    {
        // Delete the whole block.
        ++it_erase_end;
    }
    else
    {
        size_type size_to_erase = end_row - start_row_in_block2 + 1;
        blk->m_size -= size_to_erase;
        if (blk->mp_data)
        {
            // Erase the upper part.
            element_block_func::overwrite_values(*blk->mp_data, 0, size_to_erase);
            element_block_func::erase(*blk->mp_data, 0, size_to_erase);
        }
    }

    // Get the index of the block that sits before the blocks being erased.
    block_pos1 = std::distance(m_blocks.begin(), it_erase_begin);
    if (block_pos1 > 0)
        --block_pos1;

    // Now, erase all blocks in between.
    delete_element_blocks(it_erase_begin, it_erase_end);
    m_blocks.erase(it_erase_begin, it_erase_end);
    m_cur_size -= end_row - start_row + 1;

    if (!m_blocks.empty())
        merge_with_next_block(block_pos1);
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::erase_in_single_block(
    size_type start_pos, size_type end_pos, size_type block_pos, size_type start_pos_in_block)
{
    // Range falls within the same block.
    block* blk = &m_blocks[block_pos];
    size_type size_to_erase = end_pos - start_pos + 1;
    if (blk->mp_data)
    {
        // Erase data in the data block.
        size_type offset = start_pos - start_pos_in_block;
        element_block_func::overwrite_values(*blk->mp_data, offset, size_to_erase);
        element_block_func::erase(*blk->mp_data, offset, size_to_erase);
    }

    blk->m_size -= size_to_erase;
    m_cur_size -= size_to_erase;

    if (blk->m_size)
        // Block still contains data.  Bail out.
        return;

    // Delete the current block since it's become empty.
    delete_element_block(*blk);
    m_blocks.erase(m_blocks.begin()+block_pos);
    // No need to update blk_index which is not used again.

    if (block_pos == 0 || block_pos >= m_blocks.size())
        // Deleted block was either the first or the last block.
        return;

    // Check the previous and next blocks to see if they should be merged.
    block* blk_prev = &m_blocks[block_pos-1];
    block* blk_next = &m_blocks[block_pos];
    if (blk_prev->mp_data)
    {
        // Previous block has data.
        if (!blk_next->mp_data)
            // Next block is empty.  Nothing to do.
            return;

        element_category_type cat1 = mdds::mtv::get_block_type(*blk_prev->mp_data);
        element_category_type cat2 = mdds::mtv::get_block_type(*blk_next->mp_data);
        if (cat1 == cat2)
        {
            // Merge the two blocks.
            element_block_func::append_values_from_block(*blk_prev->mp_data, *blk_next->mp_data);
            blk_prev->m_size += blk_next->m_size;
            // Resize to 0 to prevent deletion of cells in case of managed cells.
            element_block_func::resize_block(*blk_next->mp_data, 0);
            delete_element_block(*blk_next);
            m_blocks.erase(m_blocks.begin()+block_pos);
        }
    }
    else
    {
        // Previous block is empty.
        if (blk_next->mp_data)
            // Next block is not empty.  Nothing to do.
            return;

        // Both blocks are empty.  Simply increase the size of the
        // previous block.
        blk_prev->m_size += blk_next->m_size;
        delete_element_block(*blk_next);
        m_blocks.erase(m_blocks.begin()+block_pos);
    }
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::insert_empty(size_type pos, size_type length)
{
    if (!length)
        // Nothing to insert.
        return end();

    size_type start_pos = 0, block_index = 0;
    if (!get_block_position(pos, start_pos, block_index))
        detail::throw_block_position_not_found("multi_type_vector::insert_empty", __LINE__, pos, block_size(), size());

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    std::ostringstream os_prev_block;
    dump_blocks(os_prev_block);
#endif

    iterator ret = insert_empty_impl(pos, start_pos, block_index, length);

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    if (!check_block_integrity())
    {
        cerr << "block integrity check failed in insert_empty (pos=" << pos << ",length=" << length << ")" << endl;
        cerr << "previous block state:" << endl;
        cerr << os_prev_block.str();
        abort();
    }
#endif

    return ret;
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::insert_empty(const iterator& pos_hint, size_type pos, size_type length)
{
    if (!length)
        // Nothing to insert.
        return end();

    size_type start_pos = 0, block_index = 0;
    get_block_position(pos_hint, pos, start_pos, block_index);

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    std::ostringstream os_prev_block;
    dump_blocks(os_prev_block);
#endif

    iterator ret = insert_empty_impl(pos, start_pos, block_index, length);

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    if (!check_block_integrity())
    {
        cerr << "block integrity check failed in insert_empty (pos=" << pos << ",length=" << length << ")" << endl;
        cerr << "previous block state:" << endl;
        cerr << os_prev_block.str();
        abort();
    }
#endif

    return ret;
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::insert_empty_impl(
    size_type pos, size_type start_pos, size_type block_index, size_type length)
{
    assert(pos < m_cur_size);

    block* blk = &m_blocks[block_index];
    if (!blk->mp_data)
    {
        // Insertion point is already empty.  Just expand its size and be done
        // with it.
        blk->m_size += length;
        m_cur_size += length;
        return get_iterator(block_index, start_pos);
    }

    if (start_pos == pos)
    {
        // Insertion point is at the top of an existing non-empty block.
        block* blk_prev = get_previous_block_of_type(block_index, mtv::element_type_empty);
        if (blk_prev)
        {
            assert(!blk_prev->mp_data);
            // Previous block is empty.  Expand the size of the previous
            // block and bail out.
            size_type offset = blk_prev->m_size;
            blk_prev->m_size += length;
            m_cur_size += length;
            return get_iterator(block_index-1, pos-offset);
        }

        // Insert a new empty block.
        m_blocks.emplace(m_blocks.begin()+block_index, length);
        m_cur_size += length;
        return get_iterator(block_index, pos);
    }

    assert(blk->mp_data);
    assert(pos > start_pos);

    size_type size_blk_prev = pos - start_pos;
    size_type size_blk_next = blk->m_size - size_blk_prev;

    // Insert two new blocks below the current; one for the empty block being
    // inserted, and the other for the lower part of the current non-empty
    // block.
    m_blocks.insert(m_blocks.begin()+block_index+1, 2u, block());

    blk = &m_blocks[block_index]; // The old pointer is invalid.
    m_blocks[block_index+1].m_size = length;
    m_blocks[block_index+2].m_size = size_blk_next;

    block* blk_next = &m_blocks[block_index+2];
    blk_next->mp_data =
        element_block_func::create_new_block(mdds::mtv::get_block_type(*blk->mp_data), 0);
    m_hdl_event.element_block_acquired(blk_next->mp_data);

    // Check if the previous block is the biger one
    if (size_blk_prev > size_blk_next)
    {
        // Upper (previous) block is larger than the lower (next) block. Copy
        // the lower values to the next block.
        element_block_func::assign_values_from_block(*blk_next->mp_data, *blk->mp_data, size_blk_prev, size_blk_next);
        element_block_func::resize_block(*blk->mp_data, size_blk_prev);
        blk->m_size = size_blk_prev;
    } 
    else 
    {
        // Lower (next) block is larger than the upper (previous) block. Copy
        // the upper values to the "next" block.
        element_block_func::assign_values_from_block(*blk_next->mp_data, *blk->mp_data, 0, size_blk_prev);
        blk_next->m_size = size_blk_prev;

        // Remove the copied values and push the rest to the top.
        element_block_func::erase(*blk->mp_data, 0, size_blk_prev);

        // Set the size of the current block to its new size ( what is after the new block )
        blk->m_size = size_blk_next;

        // And now let's swap the blocks...
        blk->swap(*blk_next);
    }

    m_cur_size += length;

    return get_iterator(block_index+1, pos);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
bool multi_type_vector<_CellBlockFunc, _EventFunc>::set_cells_precheck(
    size_type pos, const _T& it_begin, const _T& it_end, size_type& end_pos)
{
    size_type length = std::distance(it_begin, it_end);
    if (!length)
        // empty data array.  nothing to do.
        return false;

    end_pos = pos + length - 1;
    if (end_pos >= m_cur_size)
        throw std::out_of_range("Data array is too long.");

    return true;
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set_cells_impl(
    size_type row, size_type end_row, size_type start_row1, size_type block_index1, const _T& it_begin, const _T& it_end)
{
    size_type start_row2 = start_row1;
    size_type block_index2 = block_index1;
    if (!get_block_position(end_row, start_row2, block_index2))
        detail::throw_block_position_not_found("multi_type_vector::set_cells_impl", __LINE__, end_row, block_size(), size());

    if (block_index1 == block_index2)
    {
        // The whole data array will fit in a single block.
        return set_cells_to_single_block(row, end_row, block_index1, start_row1, it_begin, it_end);
    }

    return set_cells_to_multi_blocks(
        row, end_row, block_index1, start_row1, block_index2, start_row2, it_begin, it_end);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::insert_cells_impl(
    size_type row, size_type start_row, size_type block_index, const _T& it_begin, const _T& it_end)
{
    size_type length = std::distance(it_begin, it_end);
    if (!length)
        // empty data array.  nothing to do.
        return end();

    element_category_type cat = mdds_mtv_get_element_type(*it_begin);
    block* blk = &m_blocks[block_index];
    if (!blk->mp_data)
    {
        if (row == start_row)
        {
            // Insert into an empty block.  Check the previos block (if
            // exists) to see if the data can be appended to it if inserting
            // at the top of the block.
            block* blk0 = get_previous_block_of_type(block_index, cat);
            if (blk0)
            {
                // Append to the previous block.
                mdds_mtv_append_values(*blk0->mp_data, *it_begin, it_begin, it_end);
                size_type offset = blk0->m_size;
                blk0->m_size += length;
                m_cur_size += length;

                return get_iterator(block_index-1, start_row-offset);
            }

            // Just insert a new block before the current block.
            m_blocks.emplace(m_blocks.begin()+block_index, length);
            blk = &m_blocks[block_index];
            blk->mp_data = element_block_func::create_new_block(cat, 0);
            m_hdl_event.element_block_acquired(blk->mp_data);
            mdds_mtv_assign_values(*blk->mp_data, *it_begin, it_begin, it_end);
            blk->m_size = length;
            m_cur_size += length;

            return get_iterator(block_index, start_row);
        }

        insert_cells_to_middle(row, block_index, start_row, it_begin, it_end);
        m_cur_size += length;

        return get_iterator(block_index+1, row);
    }

    assert(blk->mp_data);
    element_category_type blk_cat = mdds::mtv::get_block_type(*blk->mp_data);
    if (cat == blk_cat)
    {
        // Simply insert the new data series into existing block.
        assert(it_begin != it_end);
        mdds_mtv_insert_values(*blk->mp_data, row-start_row, *it_begin, it_begin, it_end);
        blk->m_size += length;
        m_cur_size += length;
        return get_iterator(block_index, start_row);
    }

    assert(cat != blk_cat);
    if (row == start_row)
    {
        // Check the previous block to see if we can append the data there.
        block* blk0 = get_previous_block_of_type(block_index, cat);
        if (blk0)
        {
            // Append to the previous block.
            size_type offset = blk0->m_size;
            mdds_mtv_append_values(*blk0->mp_data, *it_begin, it_begin, it_end);
            blk0->m_size += length;
            m_cur_size += length;
            return get_iterator(block_index-1, start_row-offset);
        }

        // Just insert a new block before the current block.
        m_blocks.emplace(m_blocks.begin()+block_index, length);
        blk = &m_blocks[block_index];
        blk->mp_data = element_block_func::create_new_block(cat, 0);
        m_hdl_event.element_block_acquired(blk->mp_data);
        mdds_mtv_assign_values(*blk->mp_data, *it_begin, it_begin, it_end);
        blk->m_size = length;
        m_cur_size += length;

        return get_iterator(block_index, start_row);
    }

    insert_cells_to_middle(row, block_index, start_row, it_begin, it_end);
    m_cur_size += length;

    return get_iterator(block_index+1, row);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
void multi_type_vector<_CellBlockFunc, _EventFunc>::insert_cells_to_middle(
    size_type row, size_type block_index, size_type start_row,
    const _T& it_begin, const _T& it_end)
{
    size_type length = std::distance(it_begin, it_end);
    element_category_type cat = mdds_mtv_get_element_type(*it_begin);

    // Insert two new blocks.
    size_type n1 = row - start_row;
    size_type n2 = m_blocks[block_index].m_size - n1;
    m_blocks.insert(m_blocks.begin()+block_index+1, 2u, block());
    block* blk = &m_blocks[block_index];
    blk->m_size = n1;

    m_blocks[block_index+1].m_size = length;
    m_blocks[block_index+2].m_size = n2;

    // block for data series.
    block* blk2 = &m_blocks[block_index+1];
    blk2->mp_data = element_block_func::create_new_block(cat, 0);
    m_hdl_event.element_block_acquired(blk2->mp_data);
    mdds_mtv_assign_values(*blk2->mp_data, *it_begin, it_begin, it_end);

    if (blk->mp_data)
    {
        element_category_type blk_cat = mdds::mtv::get_block_type(*blk->mp_data);

        // block to hold data from the lower part of the existing block.
        block* blk3 = &m_blocks[block_index+2];
        blk3->mp_data = element_block_func::create_new_block(blk_cat, 0);
        m_hdl_event.element_block_acquired(blk3->mp_data);

        // Transfer the lower part of the current block to the new block.
        size_type offset = row - start_row;
        element_block_func::assign_values_from_block(*blk3->mp_data, *blk->mp_data, offset, n2);
        element_block_func::resize_block(*blk->mp_data, blk->m_size);
    }
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::block&
multi_type_vector<_CellBlockFunc, _EventFunc>::set_new_block_to_middle(
    size_type block_index, size_type offset, size_type new_block_size, bool overwrite)
{
    assert(block_index < m_blocks.size());

    // First, insert two new blocks at position past the current block.
    size_type lower_block_size = m_blocks[block_index].m_size - offset - new_block_size;
    m_blocks.insert(m_blocks.begin()+block_index+1, 2u, block());
    m_blocks[block_index+1].m_size = new_block_size; // empty block.
    m_blocks[block_index+2].m_size = lower_block_size;

    block& blk = m_blocks[block_index];

    if (blk.mp_data)
    {
        size_type lower_data_start = offset + new_block_size;
        block& blk_lower = m_blocks[block_index+2];
        assert(blk_lower.m_size == lower_block_size);
        element_category_type cat = mtv::get_block_type(*blk.mp_data);
        blk_lower.mp_data = element_block_func::create_new_block(cat, 0);
        m_hdl_event.element_block_acquired(blk_lower.mp_data);

        // Try to copy the fewer amount of data to the new non-empty block.
        if (offset > lower_block_size) 
        {
            // Keep the upper values in the current block and copy the lower
            // values to the new non-empty block.
            element_block_func::assign_values_from_block(
                *blk_lower.mp_data, *blk.mp_data, lower_data_start, lower_block_size);

            if (overwrite)
            {
                // Overwrite cells that will become empty.
                element_block_func::overwrite_values(*blk.mp_data, offset, new_block_size);
            }

            // Shrink the current data block.
            element_block_func::resize_block(*blk.mp_data, offset);
            blk.m_size = offset;
            blk_lower.m_size = lower_block_size;
        } 
        else 
        {
            // Keep the lower values in the current block and copy the upper
            // values to the new non-empty block (blk_lower), and swap the two
            // later.
            element_block_func::assign_values_from_block(*blk_lower.mp_data, *blk.mp_data, 0, offset);
            blk_lower.m_size = offset;

            if (overwrite)
            {
                // Overwrite cells that will become empty.
                element_block_func::overwrite_values(*blk.mp_data, offset, new_block_size);
            }

            // Remove the upper and middle values and push the rest to the top.
            element_block_func::erase(*blk.mp_data, 0, lower_data_start);

            // Set the size of the current block to its new size ( what is after the new block )
            blk.m_size = lower_block_size;
            blk_lower.m_size = offset;

            // And now let's swap the blocks...
            blk.swap(blk_lower);
        }
    }
    else
    {
        // There is no data, we just need to update the size of the block
        blk.m_size = offset;
    }
    
    return m_blocks[block_index+1];
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::block*
multi_type_vector<_CellBlockFunc, _EventFunc>::get_previous_block_of_type(
    size_type block_index, element_category_type cat)
{
    if (block_index == 0)
        // No previous block.
        return nullptr;

    block& blk = m_blocks[block_index-1];
    if (blk.mp_data)
        return (cat == mtv::get_block_type(*blk.mp_data)) ? &blk : nullptr;

    return (cat == mtv::element_type_empty) ? &blk : nullptr;
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::block*
multi_type_vector<_CellBlockFunc, _EventFunc>::get_next_block_of_type(
    size_type block_index, element_category_type cat)
{
    if (block_index == m_blocks.size()-1)
        // No next block.
        return nullptr;

    block* blk = &m_blocks[block_index+1];
    if (blk->mp_data)
        return (cat == mtv::get_block_type(*blk->mp_data)) ? blk : nullptr;

    return (cat == mtv::element_type_empty) ? blk : nullptr;
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::element_block_type*
multi_type_vector<_CellBlockFunc, _EventFunc>::exchange_elements(
    const element_block_type& src_data, size_type src_offset, size_type dst_index,
    size_type dst_offset, size_type len)
{
    assert(dst_index < m_blocks.size());
    block* blk = &m_blocks[dst_index];
    element_category_type cat_src = mtv::get_block_type(src_data);
    block* blk_next = get_next_block_of_type(dst_index, cat_src);

    if (dst_offset == 0)
    {
        // Set elements to the top of the destination block.
        block* blk_prev = get_previous_block_of_type(dst_index, cat_src);

        if (blk->m_size == len)
        {
            // The whole block will get replaced.
            std::unique_ptr<element_block_type, element_block_deleter> data(blk->mp_data);
            m_hdl_event.element_block_released(blk->mp_data);
            blk->mp_data = nullptr; // Prevent its deletion when the parent block gets deleted.

            if (blk_prev)
            {
                // Append to the previous block. Remove the current block.
                element_block_func::append_values_from_block(*blk_prev->mp_data, src_data, src_offset, len);
                blk_prev->m_size += len;
                typename blocks_type::iterator it = m_blocks.begin();
                std::advance(it, dst_index);
                typename blocks_type::iterator it_end = it;
                ++it_end;

                assert(!blk->mp_data);
                // no need to call delete_block since mp_data is null.

                if (blk_next)
                {
                    // Apend elements from the next block too.
                    element_block_func::append_values_from_block(*blk_prev->mp_data, *blk_next->mp_data);
                    blk_prev->m_size += blk_next->m_size;
                    ++it_end;
                    delete_element_block(*blk_next);
                }

                m_blocks.erase(it, it_end);
                return data.release();
            }

            // Check the next block to see if we need to merge.
            if (blk_next)
            {
                // We need to merge with the next block.  Remove the current
                // block and use the next block to store the new elements as
                // well as the existing ones.
                element_block_func::prepend_values_from_block(*blk_next->mp_data, src_data, src_offset, len);
                blk_next->m_size += len;
                m_blocks.erase(m_blocks.begin()+dst_index);
            }
            else
            {
                blk->mp_data = element_block_func::create_new_block(cat_src, 0);
                m_hdl_event.element_block_acquired(blk->mp_data);
                assert(blk->mp_data && blk->mp_data != data.get());
                element_block_func::assign_values_from_block(*blk->mp_data, src_data, src_offset, len);
            }

            // Return this data block as-is.
            return data.release();
        }

        // New block to send back to the caller.
        std::unique_ptr<element_block_type, element_block_deleter> data(nullptr);

        if (blk->mp_data)
        {
            element_category_type cat_dst = mtv::get_block_type(*blk->mp_data);
            data.reset(element_block_func::create_new_block(cat_dst, 0));

            // We need to keep the tail elements of the current block.
            element_block_func::assign_values_from_block(*data, *blk->mp_data, 0, len);
            element_block_func::erase(*blk->mp_data, 0, len);
        }

        blk->m_size -= len;

        if (blk_prev)
        {
            // Append the new elements to the previous block.
            element_block_func::append_values_from_block(*blk_prev->mp_data, src_data, src_offset, len);
            blk_prev->m_size += len;
        }
        else
        {
            // Insert a new block to house the new elements.
            m_blocks.emplace(m_blocks.begin()+dst_index, len);
            blk = &m_blocks[dst_index];
            blk->mp_data = element_block_func::create_new_block(cat_src, 0);
            m_hdl_event.element_block_acquired(blk->mp_data);
            element_block_func::assign_values_from_block(*blk->mp_data, src_data, src_offset, len);
        }

        return data.release();
    }

    // New block to send back to the caller.
    std::unique_ptr<element_block_type, element_block_deleter> data(nullptr);

    if (blk->mp_data)
    {
        // Copy the elements of the current block to the block being returned.
        element_category_type cat_dst = mtv::get_block_type(*blk->mp_data);
        data.reset(element_block_func::create_new_block(cat_dst, 0));
        element_block_func::assign_values_from_block(*data, *blk->mp_data, dst_offset, len);
    }

    assert(dst_offset > 0);
    size_type dst_end_pos = dst_offset + len;

    if (dst_end_pos == blk->m_size)
    {
        // The new elements will replace the lower part of the block.
        assert(blk->mp_data && "nullptr block mp_data");
        element_block_func::resize_block(*blk->mp_data, dst_offset);
        blk->m_size = dst_offset;

        if (blk_next)
        {
            // Merge with the next block.
            element_block_func::prepend_values_from_block(*blk_next->mp_data, src_data, src_offset, len);
            blk_next->m_size += len;
        }
        else
        {
            // Insert a new block to store the new elements.
            m_blocks.emplace(m_blocks.begin()+dst_index+1, len);
            blk = &m_blocks[dst_index+1];
            blk->mp_data = element_block_func::create_new_block(cat_src, 0);
            assert(blk->mp_data);
            m_hdl_event.element_block_acquired(blk->mp_data);
            element_block_func::assign_values_from_block(*blk->mp_data, src_data, src_offset, len);
        }
    }
    else
    {
        // The new elements will replace the middle of the block.
        assert(dst_end_pos < blk->m_size);
        blk = &set_new_block_to_middle(dst_index, dst_offset, len, false);
        assert(blk->m_size == len);
        blk->mp_data = element_block_func::create_new_block(cat_src, 0);
        assert(blk->mp_data);
        m_hdl_event.element_block_acquired(blk->mp_data);
        element_block_func::assign_values_from_block(*blk->mp_data, src_data, src_offset, len);
    }

    return data.release();
}

template<typename _CellBlockFunc, typename _EventFunc>
bool multi_type_vector<_CellBlockFunc, _EventFunc>::append_empty(size_type len)
{
    // Append empty cells.
    if (m_blocks.empty())
    {
        // No existing block. Create a new one.
        assert(m_cur_size == 0);
        m_blocks.emplace_back(len);
        m_cur_size = len;
        return true;
    }

    bool new_block_added = false;
    block* blk_last = &m_blocks.back();

    if (!blk_last->mp_data)
    {
        // Last block is empty.  Just increase its size.
        blk_last->m_size += len;
    }
    else
    {
        // Append a new empty block.
        m_blocks.emplace_back(len);
        new_block_added = true;
    }

    m_cur_size += len;

    return new_block_added;
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::exchange_elements(
    const element_block_type& src_data, size_type src_offset,
    size_type dst_index1, size_type dst_offset1, size_type dst_index2, size_type dst_offset2,
    size_type len, blocks_type& new_blocks)
{
    assert(dst_index1 < dst_index2);
    assert(dst_offset1 < m_blocks[dst_index1].m_size);
    assert(dst_offset2 < m_blocks[dst_index2].m_size);

    blocks_to_transfer bucket;
    prepare_blocks_to_transfer(bucket, dst_index1, dst_offset1, dst_index2, dst_offset2);

    m_blocks.emplace(m_blocks.begin()+bucket.insert_index, len);
    block* blk = &m_blocks[bucket.insert_index];
    blk->mp_data = element_block_func::create_new_block(mtv::get_block_type(src_data), 0);
    m_hdl_event.element_block_acquired(blk->mp_data);
    element_block_func::assign_values_from_block(*blk->mp_data, src_data, src_offset, len);
    merge_with_adjacent_blocks(bucket.insert_index);

    new_blocks.swap(bucket.blocks);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set_cells_to_single_block(
    size_type start_row, size_type end_row, size_type block_index,
    size_type start_row_in_block, const _T& it_begin, const _T& it_end)
{
    assert(it_begin != it_end);
    assert(!m_blocks.empty());

    element_category_type cat = mdds_mtv_get_element_type(*it_begin);
    block* blk = &m_blocks[block_index];
    size_type data_length = std::distance(it_begin, it_end);

    if (blk->mp_data && mdds::mtv::get_block_type(*blk->mp_data) == cat)
    {
        // simple overwrite.
        size_type offset = start_row - start_row_in_block;
        element_block_func::overwrite_values(*blk->mp_data, offset, data_length);
        if (!offset && data_length == blk->m_size)
            // Overwrite the whole block.  It's faster to use assign_values.
            mdds_mtv_assign_values(*blk->mp_data, *it_begin, it_begin, it_end);
        else
            mdds_mtv_set_values(*blk->mp_data, offset, *it_begin, it_begin, it_end);

        return get_iterator(block_index, start_row_in_block);
    }

    size_type end_row_in_block = start_row_in_block + blk->m_size - 1;
    if (start_row == start_row_in_block)
    {
        if (end_row == end_row_in_block)
        {
            // Check if we could append it to the previous block.
            size_type offset = block_index > 0 ? m_blocks[block_index-1].m_size : 0;
            if (append_to_prev_block(block_index, cat, end_row-start_row+1, it_begin, it_end))
            {
                delete_element_block(*blk);
                m_blocks.erase(m_blocks.begin()+block_index);

                // Check if we need to merge it with the next block.
                --block_index;
                merge_with_next_block(block_index);
                return get_iterator(block_index, start_row_in_block-offset);
            }

            // Replace the whole block.
            if (blk->mp_data)
            {
                m_hdl_event.element_block_released(blk->mp_data);
                element_block_func::delete_block(blk->mp_data);
            }

            blk->mp_data = element_block_func::create_new_block(cat, 0);
            m_hdl_event.element_block_acquired(blk->mp_data);
            mdds_mtv_assign_values(*blk->mp_data, *it_begin, it_begin, it_end);
            merge_with_next_block(block_index);
            return get_iterator(block_index, start_row_in_block);
        }

        // Replace the upper part of the block.

        // Shrink the current block first.
        size_type length = end_row_in_block - end_row;
        blk->m_size = length;
        if (blk->mp_data)
        {
            // Erase the upper part of the data from the current data array.
            std::unique_ptr<element_block_type, element_block_deleter> new_data(
                element_block_func::create_new_block(mdds::mtv::get_block_type(*blk->mp_data), 0));

            if (!new_data)
                throw std::logic_error("failed to instantiate a new data array.");

            size_type pos = end_row - start_row_in_block + 1;
            element_block_func::assign_values_from_block(*new_data, *blk->mp_data, pos, length);
            element_block_func::overwrite_values(*blk->mp_data, 0, pos);

            // Resize the block to zero before deleting, to prevent the
            // managed cells from being deleted when the block is deleted.
            element_block_func::resize_block(*blk->mp_data, 0);
            element_block_func::delete_block(blk->mp_data);
            blk->mp_data = new_data.release();

            // We don't call element block event listeners here.
        }

        length = end_row - start_row + 1;
        size_type offset = block_index > 0 ? m_blocks[block_index-1].m_size : 0;
        if (append_to_prev_block(block_index, cat, length, it_begin, it_end))
            return get_iterator(block_index-1, start_row_in_block-offset);

        // Insert a new block before the current block, and populate it with
        // the new data.
        m_blocks.emplace(m_blocks.begin()+block_index, length);
        blk = &m_blocks[block_index];
        blk->mp_data = element_block_func::create_new_block(cat, 0);
        m_hdl_event.element_block_acquired(blk->mp_data);
        blk->m_size = length;
        mdds_mtv_assign_values(*blk->mp_data, *it_begin, it_begin, it_end);
        return get_iterator(block_index, start_row_in_block);
    }

    assert(start_row > start_row_in_block);
    if (end_row == end_row_in_block)
    {
        // Shrink the current block and insert a new block for the new data series.
        size_type new_size = start_row - start_row_in_block;
        blk->m_size = new_size;
        if (blk->mp_data)
        {
            element_block_func::overwrite_values(*blk->mp_data, new_size, data_length);
            element_block_func::resize_block(*blk->mp_data, new_size);
        }

        new_size = end_row - start_row + 1; // size of the data array being inserted.

        if (block_index < m_blocks.size() - 1)
        {
            // Check the next block.
            block* blk_next = get_next_block_of_type(block_index, cat);
            if (blk_next)
            {
                // Prepend it to the next block.
                mdds_mtv_prepend_values(*blk_next->mp_data, *it_begin, it_begin, it_end);
                blk_next->m_size += end_row - start_row + 1;
                return get_iterator(block_index+1, start_row);
            }

            // Next block has a different data type. Do the normal insertion.
            m_blocks.emplace(m_blocks.begin()+block_index+1, new_size);
            blk = &m_blocks[block_index+1];
            blk->mp_data = element_block_func::create_new_block(cat, 0);
            m_hdl_event.element_block_acquired(blk->mp_data);
            mdds_mtv_assign_values(*blk->mp_data, *it_begin, it_begin, it_end);
            return get_iterator(block_index+1, start_row);
        }

        // Last block.
        assert(block_index == m_blocks.size() - 1);

        m_blocks.emplace_back(new_size);
        blk = &m_blocks.back();
        blk->mp_data = element_block_func::create_new_block(cat, 0);
        m_hdl_event.element_block_acquired(blk->mp_data);
        mdds_mtv_assign_values(*blk->mp_data, *it_begin, it_begin, it_end);
        return get_iterator(block_index+1, start_row);
    }

    // new data array will be in the middle of the current block.
    assert(start_row_in_block < start_row && end_row < end_row_in_block);

    block& blk_new = set_new_block_to_middle(
        block_index, start_row-start_row_in_block, end_row-start_row+1, true);

    blk_new.mp_data = element_block_func::create_new_block(cat, 0);
    m_hdl_event.element_block_acquired(blk_new.mp_data);
    mdds_mtv_assign_values(*blk_new.mp_data, *it_begin, it_begin, it_end);

    return get_iterator(block_index+1, start_row);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set_cells_to_multi_blocks(
    size_type start_row, size_type end_row,
    size_type block_index1, size_type start_row_in_block1,
    size_type block_index2, size_type start_row_in_block2,
    const _T& it_begin, const _T& it_end)
{
    assert(block_index1 < block_index2);
    assert(it_begin != it_end);
    assert(!m_blocks.empty());

    block* blk1 = &m_blocks[block_index1];
    if (blk1->mp_data)
    {
        return set_cells_to_multi_blocks_block1_non_empty(
            start_row, end_row, block_index1, start_row_in_block1,
            block_index2, start_row_in_block2, it_begin, it_end);
    }

    // Block 1 is empty.
    assert(!blk1->mp_data);

    return set_cells_to_multi_blocks_block1_non_equal(
        start_row, end_row, block_index1, start_row_in_block1,
        block_index2, start_row_in_block2, it_begin, it_end);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set_cells_to_multi_blocks_block1_non_equal(
    size_type start_row, size_type end_row,
    size_type block_index1, size_type start_row_in_block1,
    size_type block_index2, size_type start_row_in_block2,
    const _T& it_begin, const _T& it_end)
{
    element_category_type cat = mdds_mtv_get_element_type(*it_begin);
    block* blk1 = &m_blocks[block_index1];
    block* blk2 = &m_blocks[block_index2];
    size_type length = std::distance(it_begin, it_end);
    size_type offset = start_row - start_row_in_block1;
    size_type end_row_in_block2 = start_row_in_block2 + blk2->m_size - 1;

    size_type start_row_itr = start_row_in_block1;

    // Initially set to erase blocks between block 1 and block 2.
    typename blocks_type::iterator it_erase_begin = m_blocks.begin() + block_index1 + 1;
    typename blocks_type::iterator it_erase_end = m_blocks.begin() + block_index2;

    // Create the new data block first.
    block data_blk(length);

    bool blk0_copied = false;
    if (offset == 0)
    {
        // Remove block 1.
        --it_erase_begin;

        // Check the type of the previous block (block 0) if exists.
        if (block_index1 > 0)
        {
            block* blk0 = &m_blocks[block_index1-1];
            if (blk0->mp_data && cat == mdds::mtv::get_block_type(*blk0->mp_data))
            {
                // Transfer the whole data from block 0 to data block.
                data_blk.mp_data = blk0->mp_data;
                blk0->mp_data = nullptr;

                start_row_itr -= blk0->m_size;
                data_blk.m_size += blk0->m_size;
                --it_erase_begin;
                blk0_copied = true;
            }
        }
    }
    else
    {
        // Shrink block 1.
        if (blk1->mp_data)
        {
            size_type n = blk1->m_size - offset;
            element_block_func::overwrite_values(*blk1->mp_data, offset, n);
            element_block_func::resize_block(*blk1->mp_data, offset);
        }
        blk1->m_size = offset;
        start_row_itr += offset;
    }

    if (blk0_copied)
        mdds_mtv_append_values(*data_blk.mp_data, *it_begin, it_begin, it_end);
    else
    {
        data_blk.mp_data = element_block_func::create_new_block(cat, 0);
        m_hdl_event.element_block_acquired(data_blk.mp_data);
        mdds_mtv_assign_values(*data_blk.mp_data, *it_begin, it_begin, it_end);
    }

    if (end_row == end_row_in_block2)
    {
        // Remove block 2.
        ++it_erase_end;

        if (block_index2+1 < m_blocks.size())
        {
            block* blk3 = &m_blocks[block_index2+1];
            if (blk3->mp_data && mdds::mtv::get_block_type(*blk3->mp_data) == cat)
            {
                // Merge the whole block 3 with the new data. Remove block 3
                // afterward.  Resize block 3 to zero to prevent invalid free.
                element_block_func::append_values_from_block(*data_blk.mp_data, *blk3->mp_data);
                element_block_func::resize_block(*blk3->mp_data, 0);
                data_blk.m_size += blk3->m_size;
                ++it_erase_end;
            }
        }
    }
    else
    {
        bool erase_upper = true;
        if (blk2->mp_data)
        {
            element_category_type blk_cat2 = mdds::mtv::get_block_type(*blk2->mp_data);
            if (blk_cat2 == cat)
            {
                // Merge the lower part of block 2 with the new data, and
                // erase block 2.  Resize block 2 to avoid invalid free on the
                // copied portion of the block.
                size_type copy_pos = end_row - start_row_in_block2 + 1;
                size_type size_to_copy = end_row_in_block2 - end_row;
                element_block_func::append_values_from_block(
                    *data_blk.mp_data, *blk2->mp_data, copy_pos, size_to_copy);
                element_block_func::resize_block(*blk2->mp_data, copy_pos);
                data_blk.m_size += size_to_copy;

                ++it_erase_end;
                erase_upper = false;
            }
        }

        if (erase_upper)
        {
            // Erase the upper part of block 2.
            size_type size_to_erase = end_row - start_row_in_block2 + 1;
            if (blk2->mp_data)
            {
                element_block_func::overwrite_values(*blk2->mp_data, 0, size_to_erase);
                element_block_func::erase(*blk2->mp_data, 0, size_to_erase);
            }
            blk2->m_size -= size_to_erase;
        }
    }

    size_type insert_pos = std::distance(m_blocks.begin(), it_erase_begin);

    // Remove the in-between blocks first.
    delete_element_blocks(it_erase_begin, it_erase_end);
    m_blocks.erase(it_erase_begin, it_erase_end);

    // Insert the new data block.
    m_blocks.insert(m_blocks.begin()+insert_pos, std::move(data_blk));

    return get_iterator(insert_pos, start_row_itr);
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set_cells_to_multi_blocks_block1_non_empty(
    size_type start_row, size_type end_row,
    size_type block_index1, size_type start_row_in_block1,
    size_type block_index2, size_type start_row_in_block2,
    const _T& it_begin, const _T& it_end)
{
    element_category_type cat = mdds_mtv_get_element_type(*it_begin);
    block* blk1 = &m_blocks[block_index1];
    assert(blk1->mp_data);
    element_category_type blk_cat1 = mdds::mtv::get_block_type(*blk1->mp_data);

    if (blk_cat1 == cat)
    {
        block* blk2 = &m_blocks[block_index2];
        size_type length = std::distance(it_begin, it_end);
        size_type offset = start_row - start_row_in_block1;
        size_type end_row_in_block2 = start_row_in_block2 + blk2->m_size - 1;

        // Initially set to erase blocks between block 1 and block 2.
        typename blocks_type::iterator it_erase_begin = m_blocks.begin() + block_index1 + 1;
        typename blocks_type::iterator it_erase_end = m_blocks.begin() + block_index2;

        // Extend the first block to store the new data set.

        // Shrink it first to remove the old values, then append new values.
        element_block_func::overwrite_values(*blk1->mp_data, offset, blk1->m_size-offset);
        element_block_func::resize_block(*blk1->mp_data, offset);
        mdds_mtv_append_values(*blk1->mp_data, *it_begin, it_begin, it_end);
        blk1->m_size = offset + length;

        if (end_row == end_row_in_block2)
        {
            // Data overlaps the entire block 2. Erase it.
            ++it_erase_end;
        }
        else if (blk2->mp_data)
        {
            element_category_type blk_cat2 = mdds::mtv::get_block_type(*blk2->mp_data);
            if (blk_cat2 == cat)
            {
                // Copy the lower part of block 2 to the new block, and
                // remove it.  Resize block 2 to zero to prevent the
                // transferred / overwritten cells from being deleted on block
                // deletion.
                size_type data_length = end_row_in_block2 - end_row;
                size_type begin_pos = end_row - start_row_in_block2 + 1;
                element_block_func::append_values_from_block(*blk1->mp_data, *blk2->mp_data, begin_pos, data_length);
                element_block_func::overwrite_values(*blk2->mp_data, 0, begin_pos);
                element_block_func::resize_block(*blk2->mp_data, 0);
                blk1->m_size += data_length;
                ++it_erase_end;
            }
            else
            {
                // Erase the upper part of block 2.
                size_type size_to_erase = end_row - start_row_in_block2 + 1;
                element_block_func::erase(*blk2->mp_data, 0, size_to_erase);
                blk2->m_size -= size_to_erase;
            }
        }
        else
        {
            // Last block is empty.
            size_type size_to_erase = end_row - start_row_in_block2 + 1;
            blk2->m_size -= size_to_erase;
        }

        delete_element_blocks(it_erase_begin, it_erase_end);
        m_blocks.erase(it_erase_begin, it_erase_end);

        return get_iterator(block_index1, start_row_in_block1);
    }

    // The first block type is different.
    assert(blk_cat1 != cat);

    return set_cells_to_multi_blocks_block1_non_equal(
        start_row, end_row, block_index1, start_row_in_block1,
        block_index2, start_row_in_block2, it_begin, it_end);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::size_type
multi_type_vector<_CellBlockFunc, _EventFunc>::merge_with_adjacent_blocks(size_type block_index)
{
    assert(!m_blocks.empty());
    assert(block_index < m_blocks.size());
    block* blk_prev = block_index > 0 ? &m_blocks[block_index-1] : nullptr;

    if (!blk_prev)
    {
        // No previous block.
        merge_with_next_block(block_index);
        return 0;
    }

    size_type size_prev = blk_prev->m_size; // size of previous block.
    block* blk = &m_blocks[block_index];
    block* blk_next = block_index < (m_blocks.size()-1) ? &m_blocks[block_index+1] : nullptr;

    // Check the previous block.
    if (blk_prev->mp_data)
    {
        // Previous block has data.
        element_category_type cat_prev = mtv::get_block_type(*blk_prev->mp_data);
        if (!blk->mp_data || cat_prev != mtv::get_block_type(*blk->mp_data))
        {
            // Current block is empty or is of different type from the previous one.
            merge_with_next_block(block_index);
            return 0;
        }

        // Previous and current blocks are of the same type.
        if (blk_next && blk_next->mp_data && cat_prev == get_block_type(*blk_next->mp_data))
        {
            // Merge all three blocks.
            blk_prev->m_size += blk->m_size + blk_next->m_size;
            element_block_func::append_values_from_block(*blk_prev->mp_data, *blk->mp_data);
            element_block_func::append_values_from_block(*blk_prev->mp_data, *blk_next->mp_data);
            // Avoid overwriting the transferred elements.
            element_block_func::resize_block(*blk->mp_data, 0);
            element_block_func::resize_block(*blk_next->mp_data, 0);

            delete_element_block(*blk);
            delete_element_block(*blk_next);

            typename blocks_type::iterator it = m_blocks.begin();
            std::advance(it, block_index);
            typename blocks_type::iterator it_end = it;
            std::advance(it_end, 2);
            m_blocks.erase(it, it_end);
            return size_prev;
        }

        // Merge only the previous and current blocks.
        bool merged = merge_with_next_block(block_index-1);
        if (!merged)
            assert(!"Blocks were not merged!");

        return size_prev;
    }

    assert(!blk_prev->mp_data); // Previous block is empty.

    if (blk->mp_data)
    {
        // Current block is not empty. Check with the next block.
        merge_with_next_block(block_index);
        return 0;
    }

    // Previous and current blocks are both empty.
    assert(!blk->mp_data);

    if (blk_next && !blk_next->mp_data)
    {
        // Next block is empty too. Merge all three.
        blk_prev->m_size += blk->m_size + blk_next->m_size;
        // No need to call delete_element_block() since we know both blocks are empty.

        typename blocks_type::iterator it = m_blocks.begin();
        std::advance(it, block_index);
        typename blocks_type::iterator it_end = it;
        std::advance(it_end, 2);
        m_blocks.erase(it, it_end);
        return size_prev;
    }

    // Next block is not empty, or does not exist. Merge the current block with the previous one.
    bool merged = merge_with_next_block(block_index-1);
    if (!merged)
        assert(!"Blocks were not merged!");

    return size_prev;
}

template<typename _CellBlockFunc, typename _EventFunc>
bool multi_type_vector<_CellBlockFunc, _EventFunc>::merge_with_next_block(size_type block_index)
{
    assert(!m_blocks.empty());
    assert(block_index < m_blocks.size());

    if (block_index >= m_blocks.size()-1)
        // No more block below this one.
        return false;

    // Block exists below.
    block* blk = &m_blocks[block_index];
    block* blk_next = &m_blocks[block_index+1];
    if (!blk->mp_data)
    {
        // Empty block. Merge only if the next block is also empty.
        if (blk_next->mp_data)
            // Next block is not empty.
            return false;

        // Merge the two blocks.
        blk->m_size += blk_next->m_size;
        m_blocks.erase(m_blocks.begin()+block_index+1);
        return true;
    }

    if (!blk_next->mp_data)
        return false;

    if (mdds::mtv::get_block_type(*blk->mp_data) != mdds::mtv::get_block_type(*blk_next->mp_data))
        // Block types differ.  Don't merge.
        return false;

    // Merge it with the next block.
    element_block_func::append_values_from_block(*blk->mp_data, *blk_next->mp_data);
    element_block_func::resize_block(*blk_next->mp_data, 0);
    blk->m_size += blk_next->m_size;
    delete_element_block(*blk_next);
    m_blocks.erase(m_blocks.begin()+block_index+1);
    return true;
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
bool multi_type_vector<_CellBlockFunc, _EventFunc>::append_to_prev_block(
    size_type block_index, element_category_type cat, size_type length,
    const _T& it_begin, const _T& it_end)
{
    block* blk_prev = get_previous_block_of_type(block_index, cat);
    if (!blk_prev)
        return false;

    // Append to the previous block.
    mdds_mtv_append_values(*blk_prev->mp_data, *it_begin, it_begin, it_end);
    blk_prev->m_size += length;
    return true;
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::clear()
{
    delete_element_blocks(m_blocks.begin(), m_blocks.end());
    m_blocks.clear();
    m_cur_size = 0;
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::size_type
multi_type_vector<_CellBlockFunc, _EventFunc>::size() const
{
    return m_cur_size;
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::size_type
multi_type_vector<_CellBlockFunc, _EventFunc>::block_size() const
{
    return m_blocks.size();
}

template<typename _CellBlockFunc, typename _EventFunc>
bool multi_type_vector<_CellBlockFunc, _EventFunc>::empty() const
{
    return m_blocks.empty();
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::resize(size_type new_size)
{
    if (new_size == m_cur_size)
        return;

    if (!new_size)
    {
        clear();
        return;
    }

    if (new_size > m_cur_size)
    {
        // Append empty cells.
        append_empty(new_size - m_cur_size);
        return;
    }

    assert(new_size < m_cur_size && new_size > 0);

    // Find out in which block the new end row will be.
    size_type new_end_row = new_size - 1;
    size_type start_row_in_block = 0, block_index = 0;
    if (!get_block_position(new_end_row, start_row_in_block, block_index))
        detail::throw_block_position_not_found("multi_type_vector::resize", __LINE__, new_end_row, block_size(), size());

    block* blk = &m_blocks[block_index];
    size_type end_row_in_block = start_row_in_block + blk->m_size - 1;

    if (new_end_row < end_row_in_block)
    {
        // Shrink the size of the current block.
        size_type new_block_size = new_end_row - start_row_in_block + 1;
        if (blk->mp_data)
        {
            element_block_func::overwrite_values(*blk->mp_data, new_end_row+1, end_row_in_block-new_end_row);
            element_block_func::resize_block(*blk->mp_data, new_block_size);
        }
        blk->m_size = new_block_size;
    }

    // Remove all blocks that are below this one.
    typename blocks_type::iterator it = m_blocks.begin() + block_index + 1;
    delete_element_blocks(it, m_blocks.end());
    m_blocks.erase(it, m_blocks.end());
    m_cur_size = new_size;
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::swap(multi_type_vector& other)
{
    std::swap(m_cur_size, other.m_cur_size);
    m_blocks.swap(other.m_blocks);
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::swap(size_type start_pos, size_type end_pos, multi_type_vector& other, size_type other_pos)
{
    if (start_pos > end_pos)
        throw std::out_of_range("multi_type_vector::swap: start position is larger than the end position!");

    size_type other_end_pos = other_pos + end_pos - start_pos;

    if (end_pos >= m_cur_size || other_end_pos >= other.m_cur_size)
        throw std::out_of_range("multi_type_vector::swap: end position is out of bound!");

    size_type start_pos1 = 0;
    size_type block_index1 = 0;
    if (!get_block_position(start_pos, start_pos1, block_index1))
        throw std::out_of_range("multi_type_vector::swap: start block position in source not found!");

    size_type start_pos2 = start_pos1;
    size_type block_index2 = block_index1;
    if (!get_block_position(end_pos, start_pos2, block_index2))
        throw std::out_of_range("multi_type_vector::swap: end block position in source not found!");

    size_type dest_start_pos1 = 0;
    size_type dest_block_index1 = 0;
    if (!other.get_block_position(other_pos, dest_start_pos1, dest_block_index1))
        throw std::out_of_range("multi_type_vector::swap: start block position in destination not found!");

    size_type dest_start_pos2 = dest_start_pos1;
    size_type dest_block_index2 = dest_block_index1;
    if (!other.get_block_position(other_end_pos, dest_start_pos2, dest_block_index2))
        throw std::out_of_range("multi_type_vector::swap: end block position in destination not found!");

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    std::ostringstream os_prev_block, os_prev_block_other;
    dump_blocks(os_prev_block);
    other.dump_blocks(os_prev_block_other);
#endif

    swap_impl(
        other, start_pos, end_pos, other_pos, start_pos1, block_index1, start_pos2, block_index2,
        dest_start_pos1, dest_block_index1, dest_start_pos2, dest_block_index2);

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
    if (!check_block_integrity() || !other.check_block_integrity())
    {
        cerr << "block integrity check failed in swap" << endl;
        cerr << "previous block state (source):" << endl;
        cerr << os_prev_block.str();
        cerr << "previous block state (destination):" << endl;
        cerr << os_prev_block_other.str();
        abort();
    }
#endif
}

template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::shrink_to_fit()
{
    typename blocks_type::iterator it = m_blocks.begin(), it_end = m_blocks.end();
    for (; it != it_end; ++it)
    {
        block* blk = &(*it);
        assert(blk);
        if (blk->mp_data)
            element_block_func::shrink_to_fit(*blk->mp_data);
    }
}

template<typename _CellBlockFunc, typename _EventFunc>
bool multi_type_vector<_CellBlockFunc, _EventFunc>::operator== (const multi_type_vector& other) const
{
    if (this == &other)
        // Comparing to self is always equal.
        return true;

    if (m_blocks.size() != other.m_blocks.size())
        // Block sizes differ.
        return false;

    if (m_cur_size != other.m_cur_size)
        // Row sizes differ.
        return false;

    typename blocks_type::const_iterator it = m_blocks.begin(), it_end = m_blocks.end();
    typename blocks_type::const_iterator it2 = other.m_blocks.begin();
    for (; it != it_end; ++it, ++it2)
    {
        const block* blk1 = &(*it);
        const block* blk2 = &(*it2);

        if (blk1->m_size != blk2->m_size)
            // Block sizes differ.
            return false;

        if (blk1->mp_data)
        {
            if (!blk2->mp_data)
                // left is non-empty while right is empty.
                return false;
        }
        else
        {
            if (blk2->mp_data)
                // left is empty while right is non-empty.
                return false;
        }

        if (!blk1->mp_data)
        {
            assert(!blk2->mp_data);
            continue;
        }

        assert(blk1->mp_data && blk2->mp_data);
        if (!element_block_func::equal_block(*blk1->mp_data, *blk2->mp_data))
            return false;
    }

    return true;
}

template<typename _CellBlockFunc, typename _EventFunc>
bool multi_type_vector<_CellBlockFunc, _EventFunc>::operator!= (const multi_type_vector& other) const
{
    return !operator== (other);
}

template<typename _CellBlockFunc, typename _EventFunc>
multi_type_vector<_CellBlockFunc, _EventFunc>& multi_type_vector<_CellBlockFunc, _EventFunc>::operator= (const multi_type_vector& other)
{
    multi_type_vector assigned(other);
    swap(assigned);
    return *this;
}

template<typename _CellBlockFunc, typename _EventFunc>
template<typename _T>
mtv::element_t multi_type_vector<_CellBlockFunc, _EventFunc>::get_element_type(const _T& elem)
{
    return mdds_mtv_get_element_type(elem);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set_whole_block_empty(
    size_type block_index, size_type start_pos_in_block, bool overwrite)
{
    block* blk = &m_blocks[block_index];
    if (!overwrite)
        // Resize block to 0 before deleting, to prevent its elements from getting deleted.
        element_block_func::resize_block(*blk->mp_data, 0);

    delete_element_block(*blk);

    block* blk_prev = get_previous_block_of_type(block_index, mtv::element_type_empty);
    block* blk_next = get_next_block_of_type(block_index, mtv::element_type_empty);

    // Merge with adjacent block(s) if necessary.
    if (blk_prev)
    {
        assert(!blk_prev->mp_data);

        if (blk_next)
        {
            // Both preceding and next blocks are empty.
            assert(!blk_next->mp_data);

            size_type offset = blk_prev->m_size;
            blk_prev->m_size += blk->m_size + blk_next->m_size;

            // no need to call delete_block() on the current and next blocks
            // since they are empty.

            typename blocks_type::iterator it = m_blocks.begin();
            std::advance(it, block_index);
            typename blocks_type::iterator it_end = it;
            std::advance(it_end, 2);
            m_blocks.erase(it, it_end);

            return get_iterator(block_index-1, start_pos_in_block-offset);
        }

        // Only the preceding block is empty. Merge the current block with the previous.
        size_type offset = blk_prev->m_size;
        blk_prev->m_size += blk->m_size;
        typename blocks_type::iterator it = m_blocks.begin();
        std::advance(it, block_index);
        m_blocks.erase(it);

        return get_iterator(block_index-1, start_pos_in_block-offset);
    }
    else if (blk_next)
    {
        assert(!blk_next->mp_data);

        // Only the next block is empty. Merge the next block with the current.
        blk->m_size += blk_next->m_size;
        typename blocks_type::iterator it = m_blocks.begin();
        std::advance(it, block_index+1);
        m_blocks.erase(it);

        return get_iterator(block_index, start_pos_in_block);
    }

    return get_iterator(block_index, start_pos_in_block);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set_empty_in_single_block(
    size_type start_row, size_type end_row, size_type block_index, size_type start_row_in_block, bool overwrite)
{
    // Range is within a single block.
    block* blk = &m_blocks[block_index];
    if (!blk->mp_data)
        // This block is already empty.  Do nothing.
        return get_iterator(block_index, start_row_in_block);

    assert(start_row_in_block + blk->m_size >= 1);
    size_type end_row_in_block = start_row_in_block + blk->m_size - 1;
    size_type empty_block_size = end_row - start_row + 1;

    if (start_row == start_row_in_block)
    {
        // start row coincides with the start of a block.

        if (end_row == end_row_in_block)
            return set_whole_block_empty(block_index, start_row_in_block, overwrite);

        // Set the upper part of the block empty.
        if (overwrite)
            element_block_func::overwrite_values(*blk->mp_data, 0, empty_block_size);
        element_block_func::erase(*blk->mp_data, 0, empty_block_size);
        blk->m_size -= empty_block_size;

        // Check if the preceding block (if exists) is also empty.
        block* blk_prev = get_previous_block_of_type(block_index, mtv::element_type_empty);
        if (blk_prev)
        {
            // Extend the previous empty block.
            size_type offset = blk_prev->m_size;
            blk_prev->m_size += empty_block_size;
            return get_iterator(block_index-1, start_row-offset);
        }

        // Insert a new empty block before the current one.
        m_blocks.emplace(m_blocks.begin()+block_index, empty_block_size);
        return get_iterator(block_index, start_row_in_block);
    }

    if (end_row == end_row_in_block)
    {
        // end row coincides with the end of a block.
        assert(start_row > start_row_in_block);

        // Set the lower part of the block empty.
        size_type start_pos = start_row - start_row_in_block;
        if (overwrite)
            element_block_func::overwrite_values(*blk->mp_data, start_pos, empty_block_size);
        element_block_func::erase(*blk->mp_data, start_pos, empty_block_size);
        blk->m_size -= empty_block_size;

        // Check if the following block (if exists) is also empty.
        block* blk_next = get_next_block_of_type(block_index, mtv::element_type_empty);
        if (blk_next)
            // Extend the next empty block to cover the new empty segment.
            blk_next->m_size += empty_block_size;
        else
            // Insert a new empty block after the current one.
            m_blocks.emplace(m_blocks.begin()+block_index+1, empty_block_size);

        return get_iterator(block_index+1, start_row);
    }

    // Empty the middle part of a block.
    assert(end_row_in_block - end_row > 0);
    set_new_block_to_middle(block_index, start_row-start_row_in_block, empty_block_size, overwrite);

    return get_iterator(block_index+1, start_row);
}

template<typename _CellBlockFunc, typename _EventFunc>
typename multi_type_vector<_CellBlockFunc, _EventFunc>::iterator
multi_type_vector<_CellBlockFunc, _EventFunc>::set_empty_in_multi_blocks(
    size_type start_row, size_type end_row,
    size_type block_index1, size_type start_row_in_block1,
    size_type block_index2, size_type start_row_in_block2, bool overwrite)
{
    assert(block_index1 < block_index2);

    {
        // Empty the lower part of the first block.
        block* blk = &m_blocks[block_index1];
        if (blk->mp_data)
        {
            if (start_row_in_block1 == start_row)
            {
                // Empty the whole block.

                // Check if the previos block (if exists) is also empty.
                block* blk_prev = nullptr;
                if (block_index1 > 0)
                {
                    blk_prev = &m_blocks[block_index1-1];
                    if (blk_prev->mp_data)
                        // Not empty.  Ignore it.
                        blk_prev = nullptr;
                }

                if (blk_prev)
                {
                    // Previous block is empty.  Move the start row to the
                    // first row of the previous block, and make the previous
                    // block 'block 1'.
                    start_row -= blk_prev->m_size;
                    --block_index1;
                }
                else
                {
                    // Make block 1 empty.
                    if (!overwrite)
                        element_block_func::resize_block(*blk->mp_data, 0);

                    delete_element_block(*blk);
                }
            }
            else
            {
                // Empty the lower part.
                size_type new_size = start_row - start_row_in_block1;
                if (overwrite)
                    element_block_func::overwrite_values(*blk->mp_data, new_size, blk->m_size-new_size);

                element_block_func::resize_block(*blk->mp_data, new_size);
                blk->m_size = new_size;
            }
        }
        else
        {
            // First block is already empty.  Adjust the start row of the new
            // empty range.
            start_row = start_row_in_block1;
        }
    }

    size_type end_block_to_erase = block_index2; // End block position is non-inclusive.

    {
        // Empty the upper part of the last block.
        block* blk = &m_blocks[block_index2];
        size_type last_row_in_block = start_row_in_block2 + blk->m_size - 1;
        if (blk->mp_data)
        {
            if (last_row_in_block == end_row)
            {
                // Delete the whole block.
                ++end_block_to_erase;

                // Check if the following block (if exists) is also empty.
                block* blk_next = nullptr;
                if (block_index2+1 < m_blocks.size())
                {
                    blk_next = &m_blocks[block_index2+1];
                    if (blk_next->mp_data)
                        // Not empty.  Ignore it.
                        blk_next = nullptr;
                }

                if (blk_next)
                {
                    // The following block is also empty.
                    end_row += blk_next->m_size;
                    ++end_block_to_erase;
                }
            }
            else
            {
                // Empty the upper part.
                size_type size_to_erase = end_row - start_row_in_block2 + 1;
                if (overwrite)
                    element_block_func::overwrite_values(*blk->mp_data, 0, size_to_erase);

                element_block_func::erase(*blk->mp_data, 0, size_to_erase);
                blk->m_size -= size_to_erase;
            }
        }
        else
        {
            // Last block is empty.  Delete this block and adjust the end row
            // of the new empty range.
            ++end_block_to_erase;
            end_row = last_row_in_block;
        }
    }

    if (end_block_to_erase - block_index1 > 1)
    {
        // Remove all blocks in-between, from block_index1+1 to end_block_to_erase-1.

        for (size_type i = block_index1 + 1; i < end_block_to_erase; ++i)
        {
            block& blk = m_blocks[i];
            if (!overwrite && blk.mp_data)
                element_block_func::resize_block(*blk.mp_data, 0);

            delete_element_block(blk);
        }

        typename blocks_type::iterator it = m_blocks.begin() + block_index1 + 1;
        typename blocks_type::iterator it_end = m_blocks.begin() + end_block_to_erase;
        m_blocks.erase(it, it_end);
    }

    block* blk = &m_blocks[block_index1];
    size_type empty_block_size = end_row - start_row + 1;
    if (blk->mp_data)
    {
        // Insert a new empty block after the first block.
        m_blocks.emplace(m_blocks.begin()+block_index1+1, empty_block_size);
        return get_iterator(block_index1+1, start_row);
    }

    // Current block is already empty. Just extend its size.
    blk->m_size = empty_block_size;
    return get_iterator(block_index1, start_row);
}

#ifdef MDDS_MULTI_TYPE_VECTOR_DEBUG
template<typename _CellBlockFunc, typename _EventFunc>
void multi_type_vector<_CellBlockFunc, _EventFunc>::dump_blocks(std::ostream& os) const
{
    os << "--- blocks" << endl;
    for (size_type i = 0, n = m_blocks.size(); i < n; ++i)
    {
        const block* blk = &m_blocks[i];
        element_category_type cat = mtv::element_type_empty;
        if (blk->mp_data)
            cat = mtv::get_block_type(*blk->mp_data);
        os << "  block " << i << ": size=" << blk->m_size << " type=" << cat << endl;
    }
}

template<typename _CellBlockFunc, typename _EventFunc>
bool multi_type_vector<_CellBlockFunc, _EventFunc>::check_block_integrity() const
{
    if (m_blocks.empty())
        // Nothing to check.
        return true;

    if (m_blocks.size() == 1 && m_blocks[0].m_size == 0)
    {
        cerr << "block should never be zero sized!" << endl;
        return false;
    }

    const block* blk_prev = &m_blocks[0];
    if (blk_prev->m_size == 0)
    {
        cerr << "block should never be zero sized!" << endl;
        return false;
    }

    element_category_type cat_prev = mtv::element_type_empty;
    if (blk_prev->mp_data)
        cat_prev = mtv::get_block_type(*blk_prev->mp_data);

    size_type total_size = blk_prev->m_size;
    for (size_type i = 1, n = m_blocks.size(); i < n; ++i)
    {
        const block* blk = &m_blocks[i];
        if (blk->m_size == 0)
        {
            cerr << "block should never be zero sized!" << endl;
            return false;
        }

        element_category_type cat = mtv::element_type_empty;
        if (blk->mp_data)
        {
            cat = mtv::get_block_type(*blk->mp_data);

            if (element_block_func::size(*blk->mp_data) != blk->m_size)
            {
                cerr << "block size cache and the actual element block size differ!" << endl;
                return false;
            }
        }

        if (cat_prev == cat)
        {
            cerr << "Two adjacent blocks should never be of the same type." << endl;
            dump_blocks(cerr);
            return false;
        }

        blk_prev = blk;
        cat_prev = cat;

        total_size += blk->m_size;
    }

    if (total_size != m_cur_size)
    {
        cerr << "Current size does not equal the total sizes of all blocks." << endl;
        cerr << "current size=" << m_cur_size << " total block size=" << total_size << endl;
        dump_blocks(cerr);
        return false;
    }

    return true;
}
#endif

}
