Code refuses to compile when using comparator with lambda

[Remi Forax]

On 03/20/2013 11:44 AM, Maurizio Cimadamore wrote:
> So, let's rewrite your example to something self-contained which should
> have same features as yours:
>
> import java.util.*;
>
> class Test {
>       void test(List<String> ls) {
>           ls.sort(Comparators.comparing(String::length));
>       }
> }
>
>   From a type-inference point of view, this has all it needs in order to
> compile - in fact the compiler is able to type-check the method
> reference, knowing that the argument of the comparator would be a String.
>
> The problem happens with overload resolution:
>
> TestCrash.java:5: error: reference to comparing is ambiguous
>           ls.sort(Comparators.comparing(String::length));
>                              ^
>     both method <T#1>comparing(ToLongFunction<? super T#1>) in
> Comparators and method <T#2>comparing(ToDoubleFunction<? super T#2>) in
> Comparators match
>     where T#1,T#2 are type-variables:
>       T#1 extends Object declared in method
> <T#1>comparing(ToLongFunction<? super T#1>)
>       T#2 extends Object declared in method
> <T#2>comparing(ToDoubleFunction<? super T#2>)
> 1 error
>
>
> This problem is caused by a glitch in the current EDR - the most precise
> most specific check (which would allow to disambiguate between these two
> methods), is currently only applied when the argument types of the two
> applicable function descriptors are the same; it's not the case here, as
> one descriptor accepts T#1, while the other accepts T#2.
>
> The spec (and compiler) need to be updated in order to make this work.
> Good news is that we knew about this and we are working to address the
> problem.
>
> Maurizio

bitten by the wildcard capture, again :(

Rémi

>
>
> On 19/03/13 18:23, Mrityunjay Sharma wrote:
>> Hi All,
>> The below code refuses to compile when using comparator.
>>
>> *shapes1.sort(Comparators.comparing(Shape::getSize));*
>> *
>> *
>> but when i provide the type implementation (as below) of above lambda
>> expression, it works properly.
>>
>>                  *shapes1.sort(Comparators.comparing(*
>> * new ToIntFunction<Shape>() {*
>> * public int applyAsInt(Shape s) {*
>> * return s.getSize();*
>> * }}*
>> * ));*
>>
>> Please let me know if i am missing something.
>>
>> Regards,
>> MJ
>>
>