Closures prototype equivalence between closures and methodrefs

[Neal Gafter]

Alex-

In your code, doN requires its third parameter of type

{int, T => U throws X}

but you've supplied something of type

{int, String => void throws IOException}

In fact, the value you supplied is NOT a closure, it is a variable of
function type.  The closure conversion is not involved at all.

These two function types are unrelated.  There is no conversion between
them.  So the call is illegal.

In the first call, you did supply a closure (a method reference is a kind of
closure), so the closure conversion was applied.

The fact that the diagnostic prints the "required" line in terms of
javax.lang.function.OIO instead of using the function type syntax is a bug.

Regards,
Neal

On Tue, Aug 12, 2008 at 2:34 PM, Alex Buckley <Alex.Buckley at sun.com> wrote:

> Trying to stress the equivalence, I get this interesting error on the first
> line of main but not the second:
>
> A.java:13: method doN in class A cannot be applied to given types
> required: int,T,javax.lang.function.OIO<? extends U,? super T,? extends X>
> found: int,java.lang.String,{int,java.lang.String => void throws
> java.io.IOException}
>    doN(1, "hi" , closure);
>    ^
> 1 error
>
> Seems like the wrong proto-function is being selected.
>
> --
> import java.io.*;
>
> public class A {
>  static {int, String => void throws IOException} closure = {
>    int i, String s =>
>      if (i==3) throw new IOException(); System.out.println(s);
>  };
>
>  static void method(int i, String s) throws IOException {
>    if (i==3) throw new IOException(); System.out.println(s);
>  }
>
>  public static void main(String[] a) {
>    doN(1, "hi" , closure);
>    doN(2, "bye", A#method(int,String));
>  }
>
>  static <T extends String, U, throws X extends IOException>
>  void doN(int n, T x, {int, T => U throws X} b) {
>    for (int i = 0; i < n; i++) {
>      try {
>        b.invoke(i, x);
>      } catch (IOException e) { System.out.println("o no!"); }
>    }
>  }
> }
> --
>
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