My understand was, that the original proposal was to have:
merge(KStream stream);
merge(KStream... streams);
Maybe I misunderstood.
I am not really a fan of
merge(KStream stream, KStream... streams);
because it seem to break the `Collection` pattern. If I have a
collection of KStreams, I need to artificially extract one and pass as
first argument and pass all others using the second argument.
On the other hand, _if_ I have a collection, going back to the original
proposal of
merge(Collection<KStream> streams);
would work, too. Maybe bottom line is, that we might want to have both
(`Collection` and vararg) to optimize for both cases? On the other hand
it feels rather redundant? Also not sure if both are compatible?
The issue with Named is interesting. Wondering if we should just flip
the argument order:
merge(Named name, KStream... streams);
Falling back to `Collection` would also avoid this issue.
-Matthias
On 3/29/22 1:43 AM, Nick Telford wrote:
Yeah, the Named parameter makes it a little trickier. My suggestion would
be to add an additional overload that looks like:
KStream<K, V> merged(KStream<K, V> first, Named named, KStream<K, V> rest);
It's not ideal having the Named parameter split the other parameters; we
could alternatively move the Named parameter to be first, but then that
wouldn't align with the rest of the API.
Nick
On Tue, 29 Mar 2022 at 05:20, Chris Egerton <fearthecel...@gmail.com> wrote:
Hi all,
Java permits the overload. Simple test class to demonstrate:
```
public class Test {
private final String field;
public Test(String field) {
this.field = field;
}
public Test merge(Test that) {
return new Test("Single-arg merge: " + this.field + ", " +
that.field);
}
public Test merge(Test that, Test... those) {
String newField = "Varargs merge: " + this.field + ", " +
that.field;
for (Test test : those) newField += ", " + test.field;
return new Test(newField);
}
public static void main(String[] args) {
Test t1 = new Test("t1"), t2 = new Test("t2"), t3 = new Test("t3");
Test merge1 = t1.merge(t2), merge2 = t1.merge(t2, t3);
System.out.println(merge1.field); // Single-arg merge: t1, t2
System.out.println(merge2.field); // Varargs merge: t1, t2, t3
}
}
```
There's a great StackOverflow writeup on the subject [1], which explains
that during method resolution, priority is given to methods whose
signatures match the argument list without taking boxing/unboxing or
varargs into consideration:
The first phase performs overload resolution without permitting boxing or
unboxing conversion, or the use of variable arity method invocation. If no
applicable method is found during this phase then processing continues to
the second phase.
The second phase performs overload resolution while allowing boxing and
unboxing, but still precludes the use of variable arity method invocation.
If no applicable method is found during this phase then processing
continues to the third phase.
The third phase allows overloading to be combined with variable arity
methods, boxing, and unboxing.
I'm curious if it's worth keeping a variant that accepts a Named parameter?
Might be tricky to accommodate since variadic arguments have to be last.
[1] - https://stackoverflow.com/a/48850722
Cheers,
Chris
On Mon, Mar 28, 2022 at 11:46 PM Matthias J. Sax <mj...@apache.org> wrote:
I think Java does not allow to have both overloads, because it would
result in ambiguity?
If you call `s1.merge(s2)` it's unclear which method you want to call.
-Matthias
On 3/28/22 7:20 AM, Nick Telford wrote:
Hi Matthias,
How about instead of changing the signature of the existing method to
variadic, we simply add a new overload which takes variadic args:
KStream<K, V> merge(KStream<K, V> first, KStream<K, V>... rest);
That way, we maintain both source *and* binary compatibility for the
existing method, and we can enforce that there is always at least one
stream (argument) being merged.
I'm fine dropping the static methods. As you said, this is mostly all
just
syntax sugar anyway, but I do think allowing multiple streams to be
merged
together is a benefit. My motivation was that we generate diagrams for
our
Topologies, and having several binary merges becomes quite messy when a
single n-ary merge is what you're really modelling.
Regards,
Nick
On Thu, 24 Mar 2022 at 21:24, Matthias J. Sax <mj...@apache.org>
wrote:
Thanks for proposing this KIP.
I feel a little bit torn by the idea. In general, we try to keep the
surface area small, and only add APIs that delivery (significant)
value.
It seems the current proposal is more or less about syntactic sugar,
what can still be valuable, but I am not really sure about it.
I am also wondering, if we could use a variadic argument instead of a
`Collection`:
KStream<K, V> merge(KStream<K, V>... streams);
This way, we could just replace the existing method in a backward
compatible way (well, source code compatible only) and thus not
increase
the surface area of the API while still achieving your goal?
A `merge()` with zero argument would just be a no-op (same as for
using
`Collection` I assume?).
For adding the static methods: It seems not to be a common pattern to
me? I might be better not to add them and leave it to users to write a
small helper method themselves if they have such a pattern?
-Matthias
On 1/31/22 7:35 AM, Nick Telford wrote:
Hi everyone,
I'd like to discuss KIP 819:
https://cwiki.apache.org/confluence/display/KAFKA/KIP-819%3A+Merge+multiple+KStreams+in+one+operation
This is a simple KIP that adds/modifies the KStream#merge API to
enable
many streams to be merged in a single graph node.
Regards,
Nick Telford
