onecable_ios_user/Carthage/Checkouts/ReactiveCocoa/ReactiveCocoa.playground/Pages/SignalProducer.xcplaygroundpage/Contents.swift

/*:
 > # IMPORTANT: To use `ReactiveCocoa.playground`, please:
 
 1. Retrieve the project dependencies using one of the following terminal commands from the ReactiveCocoa project root directory:
    - `script/bootstrap`
    **OR**, if you have [Carthage](https://github.com/Carthage/Carthage) installed
    - `carthage checkout`
 1. Open `ReactiveCocoa.xcworkspace`
 1. Build `Result-Mac` scheme 
 1. Build `ReactiveCocoa-Mac` scheme
 1. Finally open the `ReactiveCocoa.playground`
 1. Choose `View > Show Debug Area`
 */

import Result
import ReactiveCocoa
import Foundation

/*:
 ## SignalProducer
 
 A **signal producer**, represented by the [`SignalProducer`](https://github.com/ReactiveCocoa/ReactiveCocoa/blob/master/ReactiveCocoa/Swift/SignalProducer.swift) type, creates
 [signals](https://github.com/ReactiveCocoa/ReactiveCocoa/blob/master/ReactiveCocoa/Swift/Signal.swift) and performs side effects.
 
 They can be used to represent operations or tasks, like network
 requests, where each invocation of `start()` will create a new underlying
 operation, and allow the caller to observe the result(s). The
 `startWithSignal()` variant gives access to the produced signal, allowing it to
 be observed multiple times if desired.
 
 Because of the behavior of `start()`, each signal created from the same
 producer may see a different ordering or version of events, or the stream might
 even be completely different! Unlike a plain signal, no work is started (and
 thus no events are generated) until an observer is attached, and the work is
 restarted anew for each additional observer.
 
 Starting a signal producer returns a [disposable](#disposables) that can be used to
 interrupt/cancel the work associated with the produced signal.
 
 Just like signals, signal producers can also be manipulated via primitives
 like `map`, `filter`, etc.
 Every signal primitive can be “lifted” to operate upon signal producers instead,
 using the `lift` method.
 Furthermore, there are additional primitives that control _when_ and _how_ work
 is started—for example, `times`.
 */

/*:
 ### `Subscription`
 A SignalProducer represents an operation that can be started on demand. Starting the operation returns a Signal on which the result(s) of the operation can be observed. This behavior is sometimes also called "cold". 
This means that a subscriber will never miss any values sent by the SignalProducer.
 */
scopedExample("Subscription") {
    let producer = SignalProducer<Int, NoError> { observer, _ in
        print("New subscription, starting operation")
        observer.sendNext(1)
        observer.sendNext(2)
    }
    
    let subscriber1 = Observer<Int, NoError>(next: { print("Subscriber 1 received \($0)") })
    let subscriber2 = Observer<Int, NoError>(next: { print("Subscriber 2 received \($0)") })

    print("Subscriber 1 subscribes to producer")
    producer.start(subscriber1)

    print("Subscriber 2 subscribes to producer")
    // Notice, how the producer will start the work again
    producer.start(subscriber2)
}

/*:
 ### `empty`
 A producer for a Signal that will immediately complete without sending
 any values.
 */
scopedExample("`empty`") {
    let emptyProducer = SignalProducer<Int, NoError>.empty
    
    let observer = Observer<Int, NoError>(
        failed: { _ in print("error not called") },
        completed: { print("completed called") },
        next: { _ in print("next not called") }
    )
    
    emptyProducer.start(observer)
}

/*:
 ### `never`
 A producer for a Signal that never sends any events to its observers.
 */
scopedExample("`never`") {
    let neverProducer = SignalProducer<Int, NoError>.never
    
    let observer = Observer<Int, NoError>(
        failed: { _ in print("error not called") },
        completed: { print("completed not called") },
        next: { _ in print("next not called") }
    )
    
    neverProducer.start(observer)
}

/*:
 ### `buffer`
 Creates a queue for events that replays them when new signals are
 created from the returned producer.
 
 When values are put into the returned observer (observer), they will be
 added to an internal buffer. If the buffer is already at capacity,
 the earliest (oldest) value will be dropped to make room for the new
 value.
 
 Signals created from the returned producer will stay alive until a
 terminating event is added to the queue. If the queue does not contain
 such an event when the Signal is started, all values sent to the
 returned observer will be automatically forwarded to the Signal’s
 observers until a terminating event is received.
 
 After a terminating event has been added to the queue, the observer
 will not add any further events. This _does not_ count against the
 value capacity so no buffered values will be dropped on termination.
 */
scopedExample("`buffer`") {
    let (producer, observer) = SignalProducer<Int, NoError>.buffer(1)
    
    observer.sendNext(1)
    observer.sendNext(2)
    observer.sendNext(3)
    
    var values: [Int] = []
    
    producer.start { event in
        switch event {
        case let .Next(value):
            values.append(value)
        default:
            break
        }
    }
    
    print(values)
    
    observer.sendNext(4)
    
    print(values)
}

/*:
 ### `startWithSignal`
 Creates a Signal from the producer, passes it into the given closure,
 then starts sending events on the Signal when the closure has returned.
 
 The closure will also receive a disposable which can be used to
 interrupt the work associated with the signal and immediately send an
 `Interrupted` event.
 */
scopedExample("`startWithSignal`") {
    var started = false
    var value: Int?
    
    SignalProducer<Int, NoError>(value: 42)
        .on(next: {
            value = $0
        })
        .startWithSignal { signal, disposable in
            print(value)
        }
    
    print(value)
}

/*:
 ### `startWithNext`
 Creates a Signal from the producer, then adds exactly one observer to
 the Signal, which will invoke the given callback when `next` events are
 received.
 
 Returns a Disposable which can be used to interrupt the work associated
 with the Signal, and prevent any future callbacks from being invoked.
 */
scopedExample("`startWithNext`") {
    SignalProducer<Int, NoError>(value: 42)
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `startWithCompleted`
 Creates a Signal from the producer, then adds exactly one observer to
 the Signal, which will invoke the given callback when a `completed` event is
 received.
 
 Returns a Disposable which can be used to interrupt the work associated
 with the Signal.
 */
scopedExample("`startWithCompleted`") {
    SignalProducer<Int, NoError>(value: 42)
        .startWithCompleted {
            print("completed called")
        }
}

/*:
 ### `startWithFailed`
 Creates a Signal from the producer, then adds exactly one observer to
 the Signal, which will invoke the given callback when a `failed` event is
 received.
 
 Returns a Disposable which can be used to interrupt the work associated
 with the Signal.
 */
scopedExample("`startWithFailed`") {
    SignalProducer<Int, NSError>(error: NSError(domain: "example", code: 42, userInfo: nil))
        .startWithFailed { error in
            print(error)
        }
}

/*:
 ### `startWithInterrupted`
 Creates a Signal from the producer, then adds exactly one observer to
 the Signal, which will invoke the given callback when an `interrupted` event 
 is received.
 
 Returns a Disposable which can be used to interrupt the work associated
 with the Signal.
 */
scopedExample("`startWithInterrupted`") {
    let disposable = SignalProducer<Int, NoError>.never
        .startWithInterrupted {
            print("interrupted called")
        }
    
    disposable.dispose()
}


/*:
 ### `lift`
 Lifts an unary Signal operator to operate upon SignalProducers instead.
 
 In other words, this will create a new SignalProducer which will apply
 the given Signal operator to _every_ created Signal, just as if the
 operator had been applied to each Signal yielded from start().
 */
scopedExample("`lift`") {
    var counter = 0
    let transform: Signal<Int, NoError> -> Signal<Int, NoError> = { signal in
        counter = 42
        return signal
    }
    
    SignalProducer<Int, NoError>(value: 0)
        .lift(transform)
        .startWithNext { _ in
            print(counter)
        }
}

/*:
 ### `map`
 Maps each value in the producer to a new value.
 */
scopedExample("`map`") {
    SignalProducer<Int, NoError>(value: 1)
        .map { $0 + 41 }
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `mapError`
 Maps errors in the producer to a new error.
 */
scopedExample("`mapError`") {
    SignalProducer<Int, NSError>(error: NSError(domain: "mapError", code: 42, userInfo: nil))
        .mapError { Error.Example($0.description) }
        .startWithFailed { error in
            print(error)
        }
}

/*:
 ### `filter`
 Preserves only the values of the producer that pass the given predicate.
 */
scopedExample("`filter`") {
    SignalProducer<Int, NoError>(values: [ 1, 2, 3, 4 ])
        .filter { $0 > 3}
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `take`
 Returns a producer that will yield the first `count` values from the
 input producer.
 */
scopedExample("`take`") {
    SignalProducer<Int, NoError>(values: [ 1, 2, 3, 4 ])
        .take(2)
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `observeOn`
 Forwards all events onto the given scheduler, instead of whichever
 scheduler they originally arrived upon.
 */
scopedExample("`observeOn`") {
    let baseProducer = SignalProducer<Int, NoError>(values: [ 1, 2, 3, 4 ])
    let completion = { print("is main thread? \(NSThread.currentThread().isMainThread)") }

    if #available(OSX 10.10, *) {
    baseProducer
        .observeOn(QueueScheduler(qos: QOS_CLASS_DEFAULT, name: "test"))
        .startWithCompleted(completion)
    }

    baseProducer
        .startWithCompleted(completion)
}

/*:
 ### `collect()`
 Returns a producer that will yield an array of values until it completes.
 */
scopedExample("`collect()`") {
    SignalProducer<Int, NoError> { observer, disposable in
            observer.sendNext(1)
            observer.sendNext(2)
            observer.sendNext(3)
            observer.sendNext(4)
            observer.sendCompleted()
        }
        .collect()
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `collect(count:)`
 Returns a producer that will yield an array of values until it reaches a certain count.
 */
scopedExample("`collect(count:)`") {
    SignalProducer<Int, NoError> { observer, disposable in
            observer.sendNext(1)
            observer.sendNext(2)
            observer.sendNext(3)
            observer.sendNext(4)
            observer.sendCompleted()
        }
        .collect(count: 2)
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `collect(predicate:)` matching values inclusively
 Returns a producer that will yield an array of values based on a predicate
 which matches the values collected.

 When producer completes any remaining values will be sent, the last values
 array may not match `predicate`. Alternatively, if were not collected any
 values will sent an empty array of values.
 */
scopedExample("`collect(predicate:)` matching values inclusively") {
    SignalProducer<Int, NoError> { observer, disposable in
            observer.sendNext(1)
            observer.sendNext(2)
            observer.sendNext(3)
            observer.sendNext(4)
            observer.sendCompleted()
        }
        .collect { values in values.reduce(0, combine: +) == 3 }
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `collect(predicate:)` matching values exclusively
 Returns a producer that will yield an array of values based on a predicate
 which matches the values collected and the next value.
 
 When producer completes any remaining values will be sent, the last values
 array may not match `predicate`. Alternatively, if were not collected any
 values will sent an empty array of values.
 */
scopedExample("`collect(predicate:)` matching values exclusively") {
    SignalProducer<Int, NoError> { observer, disposable in
            observer.sendNext(1)
            observer.sendNext(2)
            observer.sendNext(3)
            observer.sendNext(4)
            observer.sendCompleted()
        }
        .collect { values, next in next == 3 }
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `combineLatestWith`
 Combines the latest value of the receiver with the latest value from
 the given producer.
 
 The returned producer will not send a value until both inputs have sent at
 least one value each. If either producer is interrupted, the returned producer
 will also be interrupted.
 */
scopedExample("`combineLatestWith`") {
    let producer1 = SignalProducer<Int, NoError>(values: [ 1, 2, 3, 4 ])
    let producer2 = SignalProducer<Int, NoError>(values: [ 1, 2 ])
    
    producer1
        .combineLatestWith(producer2)
        .startWithNext { value in
            print("\(value)")
        }
}

/*:
 ### `skip`
 Returns a producer that will skip the first `count` values, then forward
 everything afterward.
 */
scopedExample("`skip`") {
    let producer1 = SignalProducer<Int, NoError>(values: [ 1, 2, 3, 4 ])
    
    producer1
        .skip(2)
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `materialize`
 
Treats all Events from the input producer as plain values, allowing them to be
manipulated just like any other value.

In other words, this brings Events “into the monad.”

When a Completed or Failed event is received, the resulting producer will send
the Event itself and then complete. When an Interrupted event is received,
the resulting producer will send the Event itself and then interrupt.
*/
scopedExample("`materialize`") {
    SignalProducer<Int, NoError>(values: [ 1, 2, 3, 4 ])
        .materialize()
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `sampleOn`
 Forwards the latest value from `self` whenever `sampler` sends a Next
 event.
 
 If `sampler` fires before a value has been observed on `self`, nothing
 happens.
 
 Returns a producer that will send values from `self`, sampled (possibly
 multiple times) by `sampler`, then complete once both input producers have
 completed, or interrupt if either input producer is interrupted.
 */
scopedExample("`sampleOn`") {
    let baseProducer = SignalProducer<Int, NoError>(values: [ 1, 2, 3, 4 ])
    let sampledOnProducer = SignalProducer<Int, NoError>(values: [ 1, 2 ])
        .map { _ in () }
    
    baseProducer
        .sampleOn(sampledOnProducer)
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `combinePrevious`
 Forwards events from `self` with history: values of the returned producer
 are a tuple whose first member is the previous value and whose second member
 is the current value. `initial` is supplied as the first member when `self`
 sends its first value.
 */
scopedExample("`combinePrevious`") {
    SignalProducer<Int, NoError>(values: [ 1, 2, 3, 4 ])
        .combinePrevious(42)
        .startWithNext { value in
            print("\(value)")
        }
}

/*:
 ### `scan`
 Aggregates `self`'s values into a single combined value. When `self` emits
 its first value, `combine` is invoked with `initial` as the first argument and
 that emitted value as the second argument. The result is emitted from the
 producer returned from `scan`. That result is then passed to `combine` as the
 first argument when the next value is emitted, and so on.
 */
scopedExample("`scan`") {
    SignalProducer<Int, NoError>(values: [ 1, 2, 3, 4 ])
        .scan(0, +)
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `reduce`
 Like `scan`, but sends only the final value and then immediately completes.
 */
scopedExample("`reduce`") {
    SignalProducer<Int, NoError>(values: [ 1, 2, 3, 4 ])
        .reduce(0, +)
        .startWithNext { value in
            print(value)
    }
}

/*:
 ### `skipRepeats`
 Forwards only those values from `self` which do not pass `isRepeat` with
 respect to the previous value. The first value is always forwarded.
 */
scopedExample("`skipRepeats`") {
    SignalProducer<Int, NoError>(values: [ 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3, 1, 1, 1, 2, 2, 2, 4 ])
        .skipRepeats(==)
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `skipWhile`
 Does not forward any values from `self` until `predicate` returns false,
 at which point the returned signal behaves exactly like `self`.
 */
scopedExample("`skipWhile`") {
    SignalProducer<Int, NoError>(values: [ 3, 3, 3, 3, 1, 2, 3, 4 ])
        .skipWhile { $0 > 2 }
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `takeUntilReplacement`
 Forwards events from `self` until `replacement` begins sending events.
 
 Returns a producer which passes through `Next`, `Failed`, and `Interrupted`
 events from `self` until `replacement` sends an event, at which point the
 returned producer will send that event and switch to passing through events
 from `replacement` instead, regardless of whether `self` has sent events
 already.
 */
scopedExample("`takeUntilReplacement`") {
    let (replacementSignal, incomingReplacementObserver) = Signal<Int, NoError>.pipe()

    let baseProducer = SignalProducer<Int, NoError> { incomingObserver, _ in
        incomingObserver.sendNext(1)
        incomingObserver.sendNext(2)
        incomingObserver.sendNext(3)

        incomingReplacementObserver.sendNext(42)

        incomingObserver.sendNext(4)

        incomingReplacementObserver.sendNext(42)
    }

    let producer = baseProducer.takeUntilReplacement(replacementSignal)
    
    producer.startWithNext { value in
        print(value)
    }
}

/*:
 ### `takeLast`
 Waits until `self` completes and then forwards the final `count` values
 on the returned producer.
 */
scopedExample("`takeLast`") {
    SignalProducer<Int, NoError>(values: [ 1, 2, 3, 4 ])
        .takeLast(2)
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `ignoreNil`
 Unwraps non-`nil` values and forwards them on the returned signal, `nil`
 values are dropped.
 */
scopedExample("`ignoreNil`") {
    SignalProducer<Int?, NoError>(values: [ nil, 1, 2, nil, 3, 4, nil ])
        .ignoreNil()
        .startWithNext { value in
            print(value)
        }
}


/*:
 ### `zipWith`
 Zips elements of two producers into pairs. The elements of any Nth pair
 are the Nth elements of the two input producers.
 */
scopedExample("`zipWith`") {
    let baseProducer = SignalProducer<Int, NoError>(values: [ 1, 2, 3, 4 ])
    let zippedProducer = SignalProducer<Int, NoError>(values: [ 42, 43 ])
    
    baseProducer
        .zipWith(zippedProducer)
        .startWithNext { value in
            print("\(value)")
        }
}

/*:
 ### `times`
 Repeats `self` a total of `count` times. Repeating `1` times results in
 an equivalent signal producer.
 */
scopedExample("`times`") {
    var counter = 0
    
    SignalProducer<(), NoError> { observer, disposable in
            counter += 1
            observer.sendCompleted()
        }
        .times(42)
        .start()
    
    print(counter)
}

/*:
 ### `retry`
 Ignores failures up to `count` times.
 */
scopedExample("`retry`") {
    var tries = 0
    
    SignalProducer<Int, NSError> { observer, disposable in
            if tries == 0 {
                tries += 1
                observer.sendFailed(NSError(domain: "retry", code: 0, userInfo: nil))
            } else {
                observer.sendNext(42)
                observer.sendCompleted()
            }
        }
        .retry(1)
        .startWithResult { result in
            print(result)
        }
}

/*:
 ### `then`
 Waits for completion of `producer`, *then* forwards all events from
 `replacement`. Any failure sent from `producer` is forwarded immediately, in
 which case `replacement` will not be started, and none of its events will be
 be forwarded. All values sent from `producer` are ignored.
 */
scopedExample("`then`") {
    let baseProducer = SignalProducer<Int, NoError>(values: [ 1, 2, 3, 4 ])
    let thenProducer = SignalProducer<Int, NoError>(value: 42)
    
    baseProducer
        .then(thenProducer)
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `replayLazily`
 Creates a new `SignalProducer` that will multicast values emitted by
 the underlying producer, up to `capacity`.
 This means that all clients of this `SignalProducer` will see the same version
 of the emitted values/errors.
 
 The underlying `SignalProducer` will not be started until `self` is started
 for the first time. When subscribing to this producer, all previous values
 (up to `capacity`) will be emitted, followed by any new values.
 
 If you find yourself needing *the current value* (the last buffered value)
 you should consider using `PropertyType` instead, which, unlike this operator,
 will guarantee at compile time that there's always a buffered value.
 This operator is not recommended in most cases, as it will introduce an implicit
 relationship between the original client and the rest, so consider alternatives
 like `PropertyType`, `SignalProducer.buffer`, or representing your stream using
 a `Signal` instead.
 
 This operator is only recommended when you absolutely need to introduce
 a layer of caching in front of another `SignalProducer`.
 
 This operator has the same semantics as `SignalProducer.buffer`.
 */
scopedExample("`replayLazily`") {
    let baseProducer = SignalProducer<Int, NoError>(values: [ 1, 2, 3, 4, 42 ])
        .replayLazily(2)
    
    baseProducer.startWithNext { value in
        print(value)
    }

    baseProducer.startWithNext { value in
        print(value)
    }

    baseProducer.startWithNext { value in
        print(value)
    }
}

/*:
 ### `flatMap(.Latest)`
 Maps each event from `self` to a new producer, then flattens the
 resulting producers (into a producer of values), according to the
 semantics of the given strategy.
 
 If `self` or any of the created producers fail, the returned producer
 will forward that failure immediately.
 */
scopedExample("`flatMap(.Latest)`") {
    SignalProducer<Int, NoError>(values: [ 1, 2, 3, 4 ])
        .flatMap(.Latest) { SignalProducer(value: $0 + 3) }
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `flatMapError`
 Catches any failure that may occur on the input producer, mapping to a new producer
 that starts in its place.
 */
scopedExample("`flatMapError`") {
    SignalProducer<Int, NSError>(error: NSError(domain: "flatMapError", code: 42, userInfo: nil))
        .flatMapError { SignalProducer<Int, NoError>(value: $0.code) }
        .startWithNext { value in
            print(value)
        }
}

/*:
 ### `sampleWith`
 Forwards the latest value from `self` with the value from `sampler` as a tuple,
 only when `sampler` sends a Next event.
 
 If `sampler` fires before a value has been observed on `self`, nothing happens.
 Returns a producer that will send values from `self` and `sampler`,
 sampled (possibly multiple times) by `sampler`, then complete once both
 input producers have completed, or interrupt if either input producer is interrupted.
 */
scopedExample("`sampleWith`") {
    let producer = SignalProducer<Int, NoError>(values: [ 1, 2, 3, 4 ])
    let sampler = SignalProducer<String, NoError>(values: [ "a", "b" ])
				
    let result = producer.sampleWith(sampler)
    
    result.startWithNext { left, right in
        print("\(left) \(right)")
    }
}

/*:
 ### `logEvents`
 Logs all events that the receiver sends.
 By default, it will print to the standard output.
 */
scopedExample("`log events`") {
    let baseProducer = SignalProducer<Int, NoError>(values: [ 1, 2, 3, 4, 42 ])
    
    baseProducer
        .logEvents(identifier: "Playground is fun!")
        .start()
}