4.0.0

This is the first release of ReactiveSwift 4.0. It requires Swift 4.1 or above.

Xcode 10 Support

1. Swift 4.2 and Xcode 10 support (#644, kudos to @ikesyo)

Operators

1. New method collect(every:on:skipEmpty:discardWhenCompleted:) which delivers all values that occurred during a time interval (#619, kudos to @Qata)
2. debounce now offers an opt-in behaviour to preserve the pending value when the signal or producer completes. You may enable it by specifying discardWhenCompleted as false (#287, kudos to @Qata)
3. New property operator: filter (#586, kudos to @iv-mexx)
4. New operator merge(with:) (#600, kudos to @ra1028)
5. New operator map(value:) (#601, kudos to @ra1028)
6. SignalProducer.merge(with:), SignalProducer.concat, SignalProducer.prefix, SignalProducer.then, SignalProducer.and, SignalProducer.or, SignalProducer.zip(with:), SignalProducer.sample(with:), SignalProducer.sample(on:), SignalProducer.take(until:), SignalProducer.take(untilReplacement:), SignalProducer.skip(until:), SignalProducer.flatMap, SignalProducer.flatMapError, SignalProducer.combineLatest(with:), Signal.flatMap, Signal.flatMapError, Signal.withLatest(from:) and Property.init(initial:then:) now accept SignalProducerConvertible conforming types (#610, #611, kudos to @ra1028)

Changes: <~ Bindings

1. <~ bindings now works with optional left-hand-side operands. (#642, kudos to @andersio and @Ankit-Aggarwal)

   let nilTarget: BindingTarget<Int>? = nil
   
   // This is now a valid binding. Previously required manual
   // unwrapping in ReactiveSwift 3.x.
   nilTarget <~ notifications.map { $0.count }

Changes: Conditional Conformance

1. For Swift 4.1 and above, BindingSource conformances are required to have Error parameterized as exactly NoError. As a result, Signal and SignalProducer are now conditionally BindingSource. (#590, kudos to @NachoSoto and @andersio)
2. For Swift 4.1 and above, Signal.Event and ActionError are now conditionally Equatable. (#590, kudos to @NachoSoto and @andersio)

Interoperability

1. Result now interoperates with SignalProducer n-ary operators as a constant producer (#606, kudos to @Qata)

Miscellaneous

1. When unfair locks from libplatform are unavailable, ReactiveSwift now fallbacks to error checking Pthread mutexes instead of the default. Mitigations regarding issues with pthread_mutex_trylock have also been applied. (#654, kudos to @andersio)
2. Lifetime may now be manually ended using Lifetime.Token.dispose(), in addition to the existing when-token-deinitializes semantic. (#641, kudos to @andersio)
3. Bag may now be initialised with a sequence of elements. (#609, kudos to @ra1028)
4. Non-class types may now conform to ReactiveExtensionProvider. (#636, kudos to @ra1028)
5. Fix some documentation errors about Carthage usage (#655)
6. [CocoaPods] CocoaPods 1.4.0 is the minimum required version. (#651, kudos to @ikesyo)