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ecj reports the commented errors on the following code, source level 1.8. Tried with versions 4.6 and 4.7M3. Compiles fine under javac 7, 8 and 9. public class Demo1 { interface MyFunction<A,B> { B apply(A a); } // Note: no problems if A doesn't have the upper bound private static class DelegatingFunction<A extends Number, B> implements MyFunction<A, B> { private final MyFunction<? super A, ? extends B> delegate; DelegatingFunction(MyFunction<? super A, ? extends B> delegate) { this.delegate = delegate; } public B apply(A t) { return this.delegate.apply(t); } } private static <A extends Number, B> DelegatingFunction<A, B> makeDelegatingFunction(MyFunction<? super A, ? extends B> delegate) { return new DelegatingFunction<A,B>(delegate); } public static <A extends Number, B> void constructor(MyFunction<? super A, ? extends B> delegate) { DelegatingFunction<A, B> f = new DelegatingFunction<>(delegate); // ERROR: Cannot infer type arguments for DelegatingFunction<> // workaround: f = new DelegatingFunction<A,B>(delegate); } public static <A extends Number, B> void genericMethod(MyFunction<? super A, ? extends B> delegate) { DelegatingFunction<A, B> f = makeDelegatingFunction(delegate); // ERROR: The method makeDelegatingFunction(MyFunction<? super A,? extends B>) in the type Demo1 // is not applicable for the arguments (MyFunction<capture#13-of ? super A,capture#14-of ? extends B>) // workaround: f = Demo1.<A,B>makeDelegatingFunction(delegate); } }
Reproduced on master.
The upper bound causes us to conclude that we have an inconsistent intersection during glb computation, and hence inference fails for the diamond. In ReferenceBinding.isConsistentIntersection, we have this line with the comment // when invoked during type inference we only want to check inconsistency among real types: if (current.isTypeVariable() || current.isWildcard() || !current.isProperType(true)) continue; In that case, we should probably apply the same rule to mostSpecific (which is taken as the first of the intersecting types, which is a CaptureBinding in this case)?
This bug hasn't had any activity in quite some time. Maybe the problem got resolved, was a duplicate of something else, or became less pressing for some reason - or maybe it's still relevant but just hasn't been looked at yet. If you have further information on the current state of the bug, please add it. The information can be, for example, that the problem still occurs, that you still want the feature, that more information is needed, or that the bug is (for whatever reason) no longer relevant. -- The automated Eclipse Genie.
Still relevant in 4.11RC2
