[rstream] Subscription without last value

[andrew8er]

I have a use case, where I do not want Subscription<A, B> to remember the last value. I just want to react to events as they happen. Currently I use this:

class AmnesticSubscriber<A, B> extends Subscription<A, B> {
	protected dispatch(x: B) {
		try {
			super.dispatch(x);
		}
		finally {
			this.last = SEMAPHORE;
		}
	}
}

But I do not think this is very elegant. How would this fit into @thi.ng/rstream?

Maybe related: #74

[postspectacular]

Hey @andrew8er - so you want to not store it in general or just avoid that new subscribers receive the last value?

[andrew8er]

For my particular use case, both approaches would solve the issue. Not storing the value would let the GC reclaim the passed value earlier if it is not referenced elsewhere.

[postspectacular]

sorry for the delay @andrew8er - I've been thinking about this and no great obvious solution to disable this yet. Been thinking about introducing ctor options objects (e.g. as done for StreamSync) more widely to configure custom behaviors like this. In the interim, one other quick-and-not-so-dirty solution would be to move the this.last setter in dispatch() into its own method, which you could then override with a blank one.

In Subscription class:

protected dispatch(x: B) {
    this.setValue(x);
    ...
}

protected setValue(x: B) {
    this.last = x;
}

Then AmnesticSubscriber only needs to:

class AmnesticSubscriber<A, B> extends Subscription<A, B> {
	protected setValue(x: B) { }
}

[andrew8er]

Ok, that would be slightly better, but I wonder if it really warrants the extra function call. Maybe I just wait for a more generic solution to this problem, I can live with mine right now.

[postspectacular]

Yep, that's what I've been wondering too. Since dispatch is a hotspot, I'd really like to keep as barebones as possible...

Let's leave this issue open as mental note. Will create a new issue about potential config options soon...