Comparators.comparing overloads

[Zhong Yu]

If we expect that applications will do a lot of comparisons on `int`
properties, this syntax

    Comparator.comparingInt(Foo::getInt)

will look very odd and funny; "int" is apparently redundant.

An ideal solution is to say that the auto-box/unbox version is less
specific, so that javac can choose the other version in overload
resolution.


Zhong Yu



On Sun, Jul 21, 2013 at 4:25 PM, Sam Pullara <spullara at gmail.com> wrote:
> I agree that this seems pretty broken to me.
>
> comparingInt
> comparingDouble
> comparingLong
>
> seem necessary to avoid this error:
>
> java: reference to comparing is ambiguous
>   both method <T>comparing(java.util.function.ToLongFunction<? super T>) in java.util.Comparator and method <T>comparing(java.util.function.ToDoubleFunction<? super T>) in java.util.Comparator match
>
> Even stranger to me is that it doesn't even mention the correct one:
>
>     public static <T> Comparator<T> comparing(ToIntFunction<? super T> keyExtractor)
>
> Good explanation for that?
>
> Currently you need to write this code like:
>
>         Comparator<String> comparator = Comparator.comparing((ToIntFunction<String>) String::length);
>
> Which seems strange when I imagine this is a common case.
>
> Sam
>
> On Jul 21, 2013, at 2:16 PM, Richard Warburton <richard.warburton at gmail.com> wrote:
>
>> Hi,
>>
>> We only mangle the name for return types, not argument types.
>>>
>>
>> Thanks for the prompt reply.
>>
>> Things still seem a little messy in this situation though.  Perhaps I've
>> missed something but we're talking about needing a cast for
>> any keyExtractor function that returns a number.  That seems to be a fairly
>> common scenario for a keyExtractor.  Suppose I want to sort Strings by
>> length, and I want to write:
>>
>> Comparator<String> comparator = comparing(String::length);
>>
>> I'll get an error telling me that the "reference to comparing is
>> ambiguous".  Now in fact I can't even hint to the compiler using a return
>> type cast as with the following snippet:
>>
>> Comparator<String> comparator = comparing(str -> (int) str.length());
>>
>> I presume this is because a cast to int can auto-box to Integer which
>> subtypes Object, so its still ambiguous between Function and ToIntFunction.
>> Again, perhaps I've missed something here, but the way to get around this
>> issue is by providing an explicit type for the keyExtractor function:
>>
>> ToIntFunction<String> lengthOfString = String::length;
>> Comparator<String> comparator = comparing(lengthOfString);
>>
>> Which really does seem less elegant to me than having overloads with
>> mangled names. As I say this isn't a weird corner case - numbers are an
>> obvious thing to use as a comparator key.
>>
>> regards,
>>
>>  Dr. Richard Warburton
>>
>>  http://insightfullogic.com
>>  @RichardWarburto <http://twitter.com/richardwarburto>
>>
>
>