javac compilation error when passing method reference to method accepting interface.
Vicente-Arturo Romero-Zaldivar
vicente.romero at oracle.com
Thu Nov 6 17:55:49 UTC 2014
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
>
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