Type cast to intersection type has no visible effect on actual type

[David Björk]

ExtendJ 8.1.2-117-g8158643 Java SE 8

‌

Type cast to intersection type has no visible effect on actual type.

Example:

import java.util.Queue;
import java.util.AbstractCollection;
import java.util.ArrayList;
import java.util.List;
import java.util.ArrayList;

public class Test {
    ArrayList<Integer> l = (AbstractCollection<Integer> & List<Integer> & Queue<Integer>) new ArrayList<Integer>();
}

Expected result:

Some form of incompatible type error. Javac generates the following error:

error: incompatible types: INT#1 cannot be converted to ArrayList<Integer>

    ArrayList<Integer> l = (AbstractCollection<Integer> & List<Integer> & Queue<Integer>) new ArrayList<Integer>();

                           ^

  where INT#1 is an intersection type:

    INT#1 extends AbstractCollection<Integer>,List<Integer>,Queue<Integer>

Actual:

No errors reported, compilation passes.

‌

Likely cause:

in java8/frontend/TypeCheck.jrag is the following code:

  syn lazy TypeDecl IntersectionCastExpr.type() = unknownType();

‌

[Jesper Öqvist]

My initial impression is that this will require several changes, and might be complicated. Two possible solutions come to mind:

• Add intersection types in the type hierarchy (as subtype of TypeDecl).
• Compute a type that matches all the types listed in the intersection type and implicitly instantiate it. This type would match the “notional class or interface” mentioned in JLS 8 4.9

‌