javac compilation error when passing method reference to method accepting interface.

[Vicente-Arturo Romero-Zaldivar]

Hi Tomasz,

Thanks for the follow-up.

Vicente

On 11/17/2014 01:00 AM, Tomasz Kowalczewski wrote:
> Thanks for looking at the issue. I have downloaded latest langtools 
> from jdk8u repo and it indeed fixes the problem.
>
>
> On Thu, Nov 6, 2014 at 6:55 PM, Vicente-Arturo Romero-Zaldivar 
> <vicente.romero at oracle.com <mailto:vicente.romero at oracle.com>> wrote:
>
>     Hi again,
>
>     By [1] I meant: https://bugs.openjdk.java.net/browse/JDK-8044546 :)
>
>     Thanks,
>     Vicente
>
>
>
>     On 11/06/2014 09:30 AM, Vicente-Arturo Romero-Zaldivar wrote:
>
>         Hi Tomasz,
>
>         The bug you are referring to has already been fixed, please
>         see [1]. The bits are not in any public release yet but you
>         can build one from the development repos:
>
>         for 8: http://hg.openjdk.java.net/jdk8u/jdk8u-dev/langtools
>         for 9: http://hg.openjdk.java.net/jdk9/dev/langtools/
>
>         Thanks,
>         Vicente
>
>         [1]
>
>         On 11/03/2014 03:15 AM, Tomasz Kowalczewski wrote:
>
>             Hi,
>
>             please excuse my ignorance if this is a known bug, was
>             discussed here or is plain silly.
>
>             I have a curious problem when calling a method with lambda
>             or method reference as an argument. This happens on
>             several versions of Java 8 including latest (u25). Test
>             case is:
>
>             package test;
>
>             import java.util.LinkedHashMap;
>             import java.util.Map;
>             import java.util.concurrent.Callable;
>
>             public class CompilationProblem {
>
>                 public void shouldCompile() {
>                     toMap(() -> new LinkedHashMap()); // Compilation error
>                     toMap(LinkedHashMap::new); // Compilation error
>                 }
>
>                 public <K, V> Map<K, V> toMap(Func0<? extends Map<K,
>             V>> mapFactory) {
>                     return null;
>                 }
>
>                 interface Func0<R> extends Callable<R> {
>
>                     public R call();
>                 }
>             }
>
>             The errors are:
>
>             Error:(10, 17) java: method toMap in class
>             pl.codewise.voluum.server.db.CompilationProblem cannot be
>             applied to given types;
>               required:
>             pl.codewise.voluum.server.db.CompilationProblem.Func0<?
>             extends java.util.Map<K,V>>
>               found: ()->new Li[...]Map()
>               reason: cannot infer type-variable(s) K,V
>                 (argument mismatch; bad return type in lambda expression
>                   java.util.LinkedHashMap cannot be converted to ?
>             extends java.util.Map<K,V>)
>
>             Error:(11, 22) java: incompatible types: no instance(s) of
>             type variable(s) K,V exist so that
>             java.util.LinkedHashMap<K,V> conforms to ? extends
>             java.util.Map<K,V>
>
>             This test case compiles if Func0 does not extend Callable.
>             How does Callable influence type inference here? What does
>             it change?
>
>             -- 
>             Regards,
>             Tomasz Kowalczewski
>
>
>
>
>
>
> -- 
> Tomasz Kowalczewski

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