valve specification
This is the engineering specification for the MotionObservable operator: valve.
Overview
valve subscribes and emits values from upstream so long as the provided stream’s last emitted
value was true.
MVP
Expose a valve operator API
Use MotionObservable to implement the operator. Accept a MotionObservable of type Bool.
class MotionObservable<T> {
public func valve(openWhenTrue valveStream: MotionObservable<Bool>) -> MotionObservable<T>
Create a nullable upstream subscription
class MotionObservable<T> {
func valve(openWhenTrue valveStream: MotionObservable<Bool>) -> MotionObservable<T>
return MotionObservable<T> { observer in
var upstreamSubscription: Subscription?
...
}
Permanently subscribe to the valve stream
Toggle the upstream subscription based on the emitted value of the valve stream. Subscribe upstream when true is received. Unsubscribe from the upstream when false is received.
class MotionObservable<T> {
func valve(openWhenTrue valveStream: MotionObservable<Bool>) -> MotionObservable<T>
return MotionObservable<T> { observer in
...
let valveSubscription = stream.subscribe { value in
let shouldOpen = value
if shouldOpen && upstreamSubscription == nil {
upstreamSubscription = self.subscribe(observer: observer)
}
if !shouldOpen && upstreamSubscription != nil {
upstreamSubscription?.unsubscribe()
upstreamSubscription = nil
}
}
}
Unsubscribe from all streams on disconnect
class MotionObservable<T> {
func valve(openWhenTrue valveStream: MotionObservable<Bool>) -> MotionObservable<T>
return MotionObservable<T> { observer in
...
return {
valveSubscription.unsubscribe()
upstreamSubscription?.unsubscribe()
upstreamSubscription = nil
}
}