SubjectLifetimeScope

Each connection will have it’s own subject instance to store replay events. Connections will be isolated from each another.

Configures the underlying implementation to behave equivalent to.

source.multicast(makeSubject: { MySubject() }).refCount()

This is the recommended default.

This has the following consequences:

• retry or concat operators will function as expected because terminating the sequence will clear internal state.
• Each connection to source observable sequence will use it’s own subject.
• When the number of subscribers drops from 1 to 0 and connection to source sequence is disposed, subject will be cleared.

let xs = Observable.deferred { () -> Observable<TimeInterval> in
        print("Performing work ...")
        return Observable.just(Date().timeIntervalSince1970)
    }
    .share(replay: 1, scope: .whileConnected)

_ = xs.subscribe(onNext: { print("next \($0)") }, onCompleted: { print("completed\n") })
_ = xs.subscribe(onNext: { print("next \($0)") }, onCompleted: { print("completed\n") })
_ = xs.subscribe(onNext: { print("next \($0)") }, onCompleted: { print("completed\n") })

Notice how time interval is different and Performing work ... is printed each time)

Performing work ...
next 1495998900.82141
completed

Performing work ...
next 1495998900.82359
completed

Performing work ...
next 1495998900.82444
completed

One subject will store replay events for all connections to source. Connections won’t be isolated from each another.

Configures the underlying implementation behave equivalent to.

source.multicast(MySubject()).refCount()

This has the following consequences:

• Using retry or concat operators after this operator usually isn’t advised.
• Each connection to source observable sequence will share the same subject.
• After number of subscribers drops from 1 to 0 and connection to source observable sequence is dispose, this operator will continue holding a reference to the same subject. If at some later moment a new observer initiates a new connection to source it can potentially receive some of the stale events received during previous connection.
• After source sequence terminates any new observer will always immediately receive replayed elements and terminal event. No new subscriptions to source observable sequence will be attempted.

let xs = Observable.deferred { () -> Observable<TimeInterval> in
        print("Performing work ...")
        return Observable.just(Date().timeIntervalSince1970)
    }
    .share(replay: 1, scope: .forever)

_ = xs.subscribe(onNext: { print("next \($0)") }, onCompleted: { print("completed\n") })
_ = xs.subscribe(onNext: { print("next \($0)") }, onCompleted: { print("completed\n") })
_ = xs.subscribe(onNext: { print("next \($0)") }, onCompleted: { print("completed\n") })

Notice how time interval is the same, replayed, and Performing work ... is printed only once

Performing work ...
next 1495999013.76356
completed

next 1495999013.76356
completed

next 1495999013.76356
completed