Filter isn't many-to-... At all, at no point it collapses a
subsequence of elements, it only works on one element at a time
I was conflating the behavior of a specific intermediate operation with
a black box view of an operation. Looking at an operation as a black box
is useless (maybe mildly interesting at most). The description of filter
as "one-to-many" threw me off balance (this is the first time I read the
gatherer spec in detail, and I've only looked at streams on an as need
basis, it took this long having brief exposures till I felt ready); but
as was said, the precise description of filter is "1-to-0..1".
I'm still curious about the idea of an "empty" input?. Seems like "many"
on the left side is never "0", in particular something like:
"1..N-to-SomeRange"
Thanks to all,
-ernie
PS. Looking at flatMap (and mapMulti) was a good exercise.
On 24/04/07 11:24 AM, Holo The Sage Wolf wrote:
Think about `flatMap` (which filter is a special case of), this is
one-to-many function that can also return 1 or 0 elements for each
input. So it makes sense to include 0 as "many".
Filter isn't many-to-... At all, at no point it collapses a
subsequence of elements, it only works on one element at a time
On Sun, 7 Apr 2024, 19:31 Ernie Rael, <err...@raelity.com> wrote:
On 24/04/07 9:11 AM, Viktor Klang wrote:
Hi Ernie,
"Many" in this case refers to "N", which is "0 ... N",
OK, I was wondering about "many" including "0".
so I'd say while it is techincally correct as-is, perhaps more
precise would be to say "1-to-0..1" gatherer, since for every
element in, there is 0 or 1 element out.
I see.
Many-to-one would be 0..N -> 1, which means that an empty input
would
"could" not "would"?
yield a single output.
Out of curiosity, is either correct technically?
Other than at initialization or finish, is it possible to have an
"empty" input?
-ernie
Cheers,
√
*
*
*Viktor Klang*
Software Architect, Java Platform Group
Oracle
------------------------------------------------------------------------
*From:* core-libs-dev <core-libs-dev-r...@openjdk.org>
<mailto:core-libs-dev-r...@openjdk.org> on behalf of Ernie Rael
<err...@raelity.com> <mailto:err...@raelity.com>
*Sent:* Sunday, 7 April 2024 18:06
*To:* core-libs-dev@openjdk.org <core-libs-dev@openjdk.org>
<mailto:core-libs-dev@openjdk.org>
*Subject:* JEP 473: Stream Gatherers (Second Preview)
This is about what might be a minor doc issue.
In https://openjdk.org/jeps/473 it says
As another example, |Stream::filter| takes a predicate that
determines whether an input element should be passed downstream;
this is simply a stateless one-to-many gatherer.
Shouldn't this be "many-to-one"?
-ernie
