FlatMapLatest with Replay - rx-swift

Question

I have a situation where I have three observables that map to a result stream.
The first observable tells me which of two other observables I should take values from. On every emission of the first observable, the result stream switches to emitting the flatmap of the appropriate observable.
This is a situation that normally can be accomplished via flatMapLatest.
However, on every switch of the flatMap, I also happen to want to replay the latest stale value. This is an issue, because flatMapLatest does not provide for an ability for a replay on old values of existing observables.
See below for an RxMarbles of what I want to accomplish:
I tried using shareReplay(N), as in the code below, but that does not seem to solve the issue.
let Observable1Replay = Observable1.share(replay: 1, scope: .forever)
let Observable2Replay = Observable2.share(replay: 1, scope: .forever)
let resultObservable = Observable3
.flatMapLatest { boolValue in
if boolValue == true {
return Observable1Replay
} else {
return Observable2Replay
}
}

Answer 1

When you are stuck, you can always roll your own and come back to it later:
func example(source: Observable<String>, obs1: Observable<String>, obs2: Observable<String>) -> Observable<String> {
return Observable.create { observer in
let lock = NSRecursiveLock()
var last1 = ""
var last2 = ""
var isFirst = false
var completeCount = 3
let srcSub = source.subscribe { event in
lock.lock(); defer { lock.unlock() }
switch event {
case .next:
isFirst = !isFirst
if isFirst && !last1.isEmpty {
observer.onNext(last1)
}
else if !isFirst && !last2.isEmpty {
observer.onNext(last2)
}
case .error(let error):
observer.onError(error)
case .completed:
completeCount -= 1
if completeCount == 0 {
observer.onCompleted()
}
}
}
let obs1Sub = obs1.subscribe { event in
lock.lock(); defer { lock.unlock() }
switch event {
case .next(let element):
if isFirst {
observer.onNext(element)
}
last1 = element
case .error(let error):
observer.onError(error)
case .completed:
completeCount -= 1
if completeCount == 0 {
observer.onCompleted()
}
}
}
let obs2Sub = obs2.subscribe { event in
lock.lock(); defer { lock.unlock() }
switch event {
case .next(let element):
if !isFirst {
observer.onNext(element)
}
last2 = element
case .error(let error):
observer.onError(error)
case .completed:
completeCount -= 1
if completeCount == 0 {
observer.onCompleted()
}
}
}
return CompositeDisposable(srcSub, obs1Sub, obs2Sub)
}
}