let replaySubject = ReplaySubject<Int>.create(bufferSize:3)
_ = replaySubject.subscribe {
    print ("first subscriber \($0)")
}
replaySubject.onNext(1)

_ = replaySubject.subscribe {
    print ("second subscriber \($0)")
}

replaySubject.onNext(2)
replaySubject.onNext(3)
_ = replaySubject.subscribe {
    print ("third subscriber \($0)")
}

replaySubject.onNext(4)