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

[Tomasz Kowalczewski]

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> 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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