Bug 460515

Description Lukas Eder 2015-02-21 11:25:21 EST

The following program doesn't compile because Y.y is invisible to X

------------------------------------------------------------
package test;

import static test.Y.y;

import java.util.function.Function;
import java.util.stream.Stream;

public class X {

    void fail() {
        Stream<Y<Integer>> stream = Stream.of(new Y<>(1));

        m(stream, (Y<Integer> y) -> y(y.y));
//      ^          ^                    ^ actual problem here (1)
//      |          +--- misleading compilation error here (2)
//      +---- additional misleading compilation error here (3)
    }

    static <T, U> void m(Stream<Y<T>> stream, Function<Y<T>, Y<U>> unzipper) {
    }
}

class Y<T> {
    private final T y;

    Y(T y) {
        this.y = y;
    }

    static <T> Y<T> y(T y) {
        return new Y<>(y);
    }
}
------------------------------------------------------------

The actual problem (1) is the fact that y.y cannot be accessed from within the lambda expression. A fix would be to make the Y.y attribute public, for instance.

But Eclipse also reports an error on the lambda argument type of Y<Integer> (2). The error message is:

> Lambda expression's parameter y is expected to be of type Y<T>

That error is incorrect, of course, and it produces a third error message (3) on the method call itself:

> The method m(Stream<Y<T>>, Function<Y<T>,Y<U>>) in the type X 
> is not applicable for the arguments 
> (Stream<Y<Integer>>, (Y<Integer> y) -> {})