OT/J Language Definition v1.3.1

<< §2.4.2 Role creation via a regular constructor

§2.4.3 Role creation in the presence of smart lifting

Explicitly instantiating a role R1 bound to a base B where smart lifting of B to R1 would actually provide a subrole R2 is dangerous: Instantiation enters the R1 into the team's internal cache. If at any time later lifting this B to R2 is requested, which is a legal request, the runtime system will answer by throwing a org.objectteams.WrongRoleException because it finds the R1 instead of the required R2. For this reason, in this specific situation the explicit instantiation new R1(..) will be flagged by a warning. The problem can be avoided by using R2 in the instantiation expression.

Example code (WrongRoleException):

public class B { void bm() {} }
public team class T {
  protected class R1 playedBy B {...}
  protected class R2 extends R1 { // inherits the binding to B
    void rm() { /* body omitted */ }
  }
  public B getDecoratedB() {
    return new R1(new B()); // compile-time warning!
  }
  public void requestLifting(B as R2 r) {}
}
// plus these calls:
T t = new T();
B b = t.getDecoratedB(); // creates an R1 for b
t.requestLifting(b); // => org.objectteams.WrongRoleException!

A note on line 8: this line passes a fresh instance of B to the lifting constructor of R1 (see §2.4.1.(b)). In order to return this B instance lowering is implicitly used for the return statement.
When line 15 is executed, a lifting of b to R2 is requested but due to line 8 an R1 is found in the internal cache.

<< §2.4.2 Role creation via a regular constructor

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1	public class B { void bm() {} }
2	public team class T {
3	protected class R1 playedBy B {...}
4	protected class R2 extends R1 { // inherits the binding to B
5	void rm() { /* body omitted */ }
6	}
7	public B getDecoratedB() {
8	return new R1(new B()); // compile-time warning!
9	}
10	public void requestLifting(B as R2 r) {}
11	}
12	// plus these calls:
13	T t = new T();
14	B b = t.getDecoratedB(); // creates an R1 for b
15	t.requestLifting(b); // => `org.objectteams.WrongRoleException!`