On Jun 18, 2018, at 2:29 PM, Brian Goetz <brian.go...@oracle.com> wrote:
"bisecting" sounds like it sends half the elements to one collector and
half to the other …
The main bisection or splitting operation that's relevant to a stream is
what
a spliterator does, so this is a concern.
Nobody has mentioned "unzipping" yet; this is a term of art which applies
to streams
of tuples. The image of a zipper is relatively clear and unambiguous, and
the tradition
is pretty strong. https://en.wikipedia.org/wiki/
Convolution_(computer_science)
The thing we are looking at differs in two ways from classic "unzipping":
First, the
two collectors themselves convert the same T elements to whatever internal
value
(T1, T2) is relevant. Second, we are looking at a new terminal operation
(a collector) which
consolidates the results from both of streams (a notional Stream<T1> and
Stream<T2>,
if you like), rather than delivering the streams as a pair of outputs.
The classic "unzip" operation applies "fst" and "snd" (or some other
conventional
set of access functions) to each T-element of the input stream. Since we
don't
have a privileged 2-tuple type (like Pair<T1,T2>) in Java, the user would
need
to nominate those two functions explicitly, either by folding them into a
"mapping"
on each collector, or as a utility overloading like this:
unzipping(
Function<? super T, T1> f1, // defaults to identity
Collector<? super T1, ?, R1> c1,
Function<? super T, T2> f2, // defaults to identity
Collector<? super T2, ?, R2> c2,
BiFunction<? super R1, ? super R2, ? extends R> finisher) {
return toBoth(mapping(f1, c1), mapping(f2, c2));
}
"tee" might be a candidate, though it doesn't follow the `ing
convention. "teeing" sounds dumb.
"tee" sounds asymmetrical. "diverting" or "detouring" are "*ing" words
that might
express asymmetrical disposition of derivative streams.
An asymmetrical operation might be interesting if it could fork off a
stream of
its own. It would have to have a side-effecting void-producing terminal
operation,
so the main (undiverted) stream could continue to progress at the top
level of
the expression.
interface Stream<T> {
default Stream<T> diverting(Consumer<Stream<T>> tee) { … }
}
values.stream().diverting(s2->s2.forEach(System.out::
println)).filter(…).collect(…);
Or (and this might be a sweet spot) a symmetric stream-tee operation could
materialize two sibling streams and rejoin their results with a bifunction:
class Collectors {
static <R1, R2, R> Stream<T> unzipping(
Function<? super Stream<T>, R1> f1,
Function<? super Stream<T>, R2> f2,
BiFunction<? super R1, ? super R2, ? extends R> finisher)
{ … }
}
values.stream().unzipping(
s1->s1.forEach(System.out::println),
s2->s2.filter(…).collect(…),
(void1, r2)->r2
);
This would allow each "fork child" of the stream to continue to use the
Stream API instead of the more restrictive Collector operators.
Optimal code generation for forked/unzipped/teed streams would be tricky,
requiring simultaneous loop control logic for each stream.
To me that's a feature, not a bug, since hand-writing ad hoc
simultaneous loops is a pain.
My $0.02.
— John
