Exploring the Signal and SignalProducer objects in ReactiveSwift 1.1

Signal vs SignalProducer.swift

import Foundation
import ReactiveSwift
import Result

let a = MutableProperty<String>("")
let b = MutableProperty<String>("")
let c = MutableProperty<String>("")

// Signals are hot
let signalDisposable = Signal.combineLatest(a.signal, b.signal, c.signal)
    .observeValues { aVal, bVal, cVal in
        print("combined signal = \(aVal + bVal + cVal)")
    }

a.value = "🍖"
b.value = "🌏"
// No output, still awaiting value from C to combine

c.value = "🐔"
// Output: combined signal = 🍖🌏🐔
// Values from all 3 signals have been sent and combined

a.value = "🍕"
// Output: combined signal = 🍕🌏🐔

signalDisposable?.dispose()
b.value = "🌞"
// No output because the combined signal has been disposed



// SignalProducers are cold
var disposable = SignalProducer.combineLatest(a.producer, b.producer, c.producer)
    .startWithValues { aVal, bVal, cVal in
        print("combined producer = \(aVal + bVal + cVal)")
    }
// Output: combined producer = 🍕🌞🐔
// SignalProducers create side-effects. The initial values are sent when the SignalProducer starts.

c.value = "😸"
// Output: combined producer = 🍕🌞😸

disposable.dispose()



// Try a mix of a producer and two signals
disposable = a.producer
    .lift { aSignal in
        return Signal.combineLatest(aSignal, b.signal, c.signal)
    }
    .startWithValues { aVal, bVal, cVal in
        print("mixed producer = \(aVal + bVal + cVal)")
    }
// Nothing is printed because signals B and C have not sent any values

b.value = "🍇"
c.value = "🍇"
// Output: mixed producer = 🍕🍇🍇
// All values have been sent (A has already sent an initial value because it's a SignalProducer)

a.value = "🍇"
// Output: mixed producer = 🍇🍇🍇