Comparators.comparing inference error
Michael Nascimento
misterm at gmail.com
Thu Apr 18 11:18:24 PDT 2013
Hi folks,
I had a comparison chain in Guava which I tried to migrate by creating
a comparator:
Comparator<YearMonthDecade> c = Comparators
.comparing(YearMonthDecade::getYearMonth)
.thenComparing(YearMonthDecade::getDecadeNumber);
getYearMonth returns a YearMonth and getDecadeNumber returns an int. I
get the following compiler error:
YearMonthDecade.java:[69,4] error: reference to comparing is ambiguous
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>)
YearMonthDecade.java:[69,14] error: incompatible types: Cannot
instantiate inference variables T because of an inference loop
I can get it to compile with:
Comparator<YearMonthDecade> c = Comparators
.<YearMonthDecade,YearMonth>comparing(YearMonthDecade::getYearMonth)
.<YearMonthDecade>thenComparing((ToIntFunction<YearMonthDecade>)
YearMonthDecade::getDecadeNumber);
Do you plan to make this work somehow (smarter compiler or no
overloading anymore)?
Regards,
Michael
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