Equivalent to Rx.Subject

Hello everyone, I’m new to most and I was wondering if there is an equivalent to Rx’s Subject? In particular, I’m curious if there is a way for recreating Rx.ReplaySubject

For some more information on what I’m trying to accomplish.

I’m trying to rewrite Cycle.js using Most instead of RxJs. I haven’t been able to find a way to recreate the circular dependency between Observables.

In Cycle.js it’s roughly like this (although a little more complex)

const sinksProxy = new Rx.Subject()
const sources = driverFn( sinkProxy )
const sinks = application( sources )
sinks.subscribe( value => sinksProxy.onNext(value) )

Thanks in advance!

[TylorS]

For anyone else looking for this, I have an implementation here https://github.com/TylorS/most-subject. In combination with https://github.com/mostjs/hold a ReplaySubject-like stream can be created though only with 1 past value, as that’s the common use case.

@briancavalier Do you think it is safe to close this?

[briancavalier]

Hey @TylorS, this is a really interesting situation–one I’ve not really thought about before. I’d love to find a way to do it declaratively, rather than having to subscribe and feed the events back in. It’s totally not obvious how to do it declaratively right now, though (but I’ll give it more thought!)

Anyway, I think it would be annoying to try to do it in the current version of most.js. There’s been some previous discussion about providing an externalized imperative event pushing api in #72. That PR is a bit long in the tooth, and should probably be abandoned, but the idea certainly seems like it’d work for what you’re doing in that sample code.

One question: How do external events make their way into the cycle? Does someone (perhaps code inside driverFn or application end up calling sinkProxy.onNext?

I went back and forth on adding an API like that, since it tends to either put the burden managing race conditions on the caller, or introduce inefficiency if you force every event to be queued and sent in a future call stack. But I’ve made my peace with it 😃

Would it work for you if there were some new API that looked like:

import most from 'most';
const { sink, stream } = most.whatever();

sink.add(x); // add x to stream

Thoughts?