On Wed, 8 Nov 2023 14:19:47 GMT, Tagir F. Valeev <tval...@openjdk.org> wrote:
>> src/java.base/share/classes/java/util/stream/Gatherer.java line 252:
>>
>>> 250: * Gatherer as input that Gatherer
>>> 251: */
>>> 252: default <AA, RR> Gatherer<T, ?, RR> andThen(Gatherer<? super R,
>>> AA, ? extends RR> that) {
>>
>> It would be great to remove AA type parameter, which is mentioned only once,
>> so could be replaced with `?`. This will improve user experience if they
>> happen to need to specify type parameters explicitly.
>
> This is especially important given that often you don't know the AA type at
> all. E.g., imagine that you are doing `.andThen(Gatherers.fold(...))`, but
> `fold` returns `Gatherer<T, ?, R>`, so you can specify explicit `RR`, but not
> `AA`.
Has this proven to be a problem for things like
[Collectors.mapping(…)](https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/stream/Collectors.html#mapping(java.util.function.Function,java.util.stream.Collector))
? 🤔
There's one implication on turning it into a wildcard—it may actually cause
issues implementing the composition directly in the override, as you won't have
a typename to refer to.
Do you have a concrete example of where the current "encoding" causes a
caller-problem?
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PR Review Comment: https://git.openjdk.org/jdk/pull/16420#discussion_r1386796562
