Odd behaviour on `on` about reactiveswift

[mdiep]

This is because of how SignalProducer.init(value:) works. It sends the value immediately.

It goes something like this.

1. Call starting
2. Call SignalProducer to start
   1. init(value:) sends a value (value) and then completes (completed)
3. Call started

[gkaimakas]

@mdiep This is quite confusing. I have observed the same behaviour on MutableProperty

[andersio]

started is invoked after the starting side effect is done. So you would exhibit the same behaviour in any producer that sends events synchronously in the start handler.

@mdiep Perhaps started should not be invoked if the produced signal is terminated in the start handler. Any thoughts?

[mdiep]

I think it'd be more surprising for started to not always fire.

[gkaimakas]

Shouldn't started fire after starting?

[andersio]

Yes in order, but it need not be immediate.

started is invoked after the starting side effect is done.

Look at the signature of SignalProducer.init(_:). It accepts a startHandler that is passed an observer. This means events can be sent as part of the starting side effect. started just indicates the side effect has completed, and it is invoked after startWithSignal (which in turn invokes the start handler) returns.

Note that starting is the good old started in RAC 4.x.

[mdiep]

Maybe this will help you make sense of it: the signal completed before it finished starting.