This would definitely be a useful addition to the public MethodHandles API. Achieving this functionality with currently available means is extremely tricky and certainly does not produce readable or maintainable code.
Hannes > Am 22.10.2018 um 14:07 schrieb Jim Laskey <james.las...@oracle.com>: > > Thank you for doing this. The MethodHandle changes will simplify many a use > case. > > Cheers, > > — Jim > > >> On Oct 22, 2018, at 6:58 AM, Claes Redestad <claes.redes...@oracle.com> >> wrote: >> >> Hi, >> >> StringConcatFactory uses a customized internal foldArguments >> implementation which takes positional arguments to avoid intermediary >> permutation steps, see JDK-8165492[1]. My intent has been to clean this >> up for possible inclusion in the public API. >> >> In preparation of that, I realized that we could probably profit from a >> filtering combinator on top of the existing folding one. Said and done: >> >> http://cr.openjdk.java.net/~redestad/8212726/jdk.00/ >> https://bugs.openjdk.java.net/browse/JDK-8212726 >> >> Using this new MethodHandles.filterArgumentsWithCombiner in place of >> MHs.dropArguments + MHs.foldArgumentsWithCombiner gets rid of a >> significant number of MethodHandles with retained performance >> characteristics. In startup tests exercising indified String >> concatenation the number of generated classes drops by ~25-30%, with a >> measurable improvement in startup time as a result. Subjectively it also >> makes the code in StringConcatFactory easier to read and follow. >> >> While this surely strengthens the case to include these in the public >> API, I'd like to move ahead with this as an internal optimization first >> and propose MethodHandles.filter-/foldArgumentsWithCombiner as public >> API points as a follow-up: apart from improving the javadoc we need to >> work out specification for corner cases - especially illegal values - >> and harden the implementation with more tests. I'm sure there might be >> opinions about the naming of these methods, too... :-) >> >> Thanks! >> >> /Claes >> >> [1] https://bugs.openjdk.java.net/browse/JDK-8165492 >
