Support .Publish(...)

[Dorus]

For reference, the Rx Design Guidelines 5.10 suggest to use this operator.

The operator .publish() returns an ConnectableObservable, this means you first need to subscribe all your sources, .connect() it, keep a reference to your connect to prevent leaks, and then you also end up with a hot observable, so downstream subscribers better be ready as well.

Most of the time you only want to duplicate a stream locally. RxJS 4 and many other Rx implementations allow you to write

xs.publish(ob => ob.zip(ob.skip(1), (x, y) => {...}))

Here we use publish to peek at the next item in the source. Another favorite of mine is

xs.publish(ob => ob.window(ob.debounce(100)))

Because often you want to use a source for its own window-boundary.

This operator is very similar to .let, but avoid subscribing to the source twice. Useful on cold observables, but also to avoid the overhead of subscribing multiple times to a hot source. (imagine you use this trick 4x in a row with let, you end up with 2^4th subscriptions.)

[kwonoj]

Would you elaborate bit more? so far I know current publish already returns ConnectableObservable (

rxjs/src/operator/publish.ts

Line 15 in 34cdef5

export function publish<T>(): ConnectableObservable<T> {

) would you mind to share some snippet of pusedo for suggested behavior?

[Dorus]

The operator publish([selector]) should not return an ConnectableObservable, instead it returns the result of creating the connectable observable, passing the connectable observable to the selector,

aka

function publish(source, selector) {
  return Rx.Observable.create(ob => {
    var xs = source.publish();
    return selector(xs).subscribe(ob).add(xs.connect());
  });
}

Similar to publish in RxJS 4 and Rx.Net.

selector
Type: System.Func<IObservable, IObservable>
The selector function which can use the multicasted source sequence as many times as needed, without causing multiple subscriptions to the source sequence.

[kwonoj]

Thanks for clarification. I actually noticed RxJS 5 missing publish accepts selector compare to RxJS 4, and wasn't able to look up reason. @staltz , @Blesh , remember there was discussions to align sharing operators in RxJS 5, is this conclusion of it or it's yet migrated from RxJS 4?

[staltz]

Yeah, I think this makes sense to implement.

[kwonoj]

I'll try to introduce those changes.

[lock]

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