Hi Nir, I think currently the most similar code pattern in stream that enjoys a
good performance is:
.<MyClass>mapMulti((x, sink) -> {
if (x instanceof MyClass myClass) {
sink.accept(myClass);
}
})
>From the language point of view, such pattern-match-and-map-0/1 operations may
>be common.
That said, can we provide a language feature in the future to convert a pattern
declaration to BiConsumer<T, XxxConsumer<args>>? I believe that is a better way
to address the question you have raised here.
Regards,
Chen Liang
________________________________
From: core-libs-dev <core-libs-dev-r...@openjdk.org> on behalf of Nir Lisker
<nlis...@gmail.com>
Sent: Saturday, April 26, 2025 1:55 PM
To: core-libs-dev@openjdk.org <core-libs-dev@openjdk.org>
Subject: Casting gatherer
Hi,
instanceof has been refitted to include an auto-cast ("pattern matching on
instanceof"). Unfortunately, doing this as an intermediate operation on a
stream requires first to filter via instanceof and then map via a cast. This is
because
x instanceof MyClass myClass
returns a boolean, not myClass.
I've asked for an easier way of doing it long ago directly on Stream and was
declined, but now with Gatherers I'm bringing this up again. I think it would
be reasonable to put such an operation in the Gatherers class. I imagine that
many Gatherer libraries, or utility classes, will include it since it's a
common operation, and having it in the JDK means that it'll be done the best
way possible (you can optimize where others can't, if applicable here).
-- Nir
