ObjectiveCBridging.md

Objective-C Bridging

While ReactiveCocoa 3.0 introduces an entirely new design, it also aims for maximum compatibility with RAC 2, to ease the pain of migration. To interoperate with RAC 2’s Objective-C APIs, RAC 3 offers bridging functions that can convert Objective-C types to Swift types and vice-versa.

Because the APIs are based on fundamentally different designs, the conversion is not always one-to-one; however, every attempt has been made to faithfully translate the concepts between the two APIs (and languages).

The bridged types include:

1. RACSignal and SignalProducer or Signal
2. RACCommand and Action
3. RACScheduler and SchedulerType
4. RACDisposable and Disposable

For the complete bridging API, including documentation, see ObjectiveCBridging.swift. To learn more about how to migrate between ReactiveCocoa 2 and 3, see the CHANGELOG.

RACSignal and SignalProducer or Signal

In RAC 3, “cold” signals are represented by the SignalProducer type, and “hot” signals are represented by the Signal type.

“Cold” RACSignals can be converted into SignalProducers using the new toSignalProducer method:

extension RACSignal {
	func toSignalProducer() -> SignalProducer<AnyObject?, NSError>
}

“Hot” RACSignals cannot be directly converted into Signals, because any RACSignal subscription could potentially involve side effects. To obtain a Signal, use RACSignal.toSignalProducer followed by SignalProducer.start, which will make those potential side effects explicit.

For the other direction, use the toRACSignal() function.

When called with a SignalProducer, these functions will create a RACSignal to start() the producer once for each subscription:

func toRACSignal<T: AnyObject, E>(producer: SignalProducer<T, E>) -> RACSignal
func toRACSignal<T: AnyObject, E>(producer: SignalProducer<T?, E>) -> RACSignal

When called with a Signal, these functions will create a RACSignal that simply observes it:

func toRACSignal<T: AnyObject, E>(signal: Signal<T, E>) -> RACSignal
func toRACSignal<T: AnyObject, E>(signal: Signal<T?, E>) -> RACSignal

RACCommand and Action

To convert RACCommands into the new Action type, use the toAction() extension method:

extension RACCommand {
	func toAction() -> Action<AnyObject?, AnyObject?, NSError>
}

To convert Actions into RACCommands, use the toRACCommand() function:

func toRACCommand<Output: AnyObject, E>(action: Action<AnyObject, Output, E>) -> RACCommand
func toRACCommand<Output: AnyObject, E>(action: Action<AnyObject?, Output, E>) -> RACCommand

NOTE: The executing properties of actions and commands are not synchronized across the API bridge. To ensure consistency, only observe the executing property from the base object (the one passed into the bridge, not retrieved from it), so updates occur no matter which object is used for execution.

RACScheduler and SchedulerType

Any RACScheduler instance is automatically a DateSchedulerType (and therefore a SchedulerType), and can be passed directly into any function or method that expects one.

Some (but not all) SchedulerTypes from RAC 3 can be converted into RACScheduler instances, using the toRACScheduler() method:

extension ImmediateScheduler {
	func toRACScheduler() -> RACScheduler
}

extension UIScheduler {
	func toRACScheduler() -> RACScheduler
}

extension QueueScheduler {
	func toRACScheduler() -> RACScheduler
}

RACDisposable and Disposable

Any RACDisposable instance is automatically a Disposable, and can be used directly anywhere a type conforming to Disposable is expected.

Although there is no direct conversion from Disposable into RACDisposable, it is easy to do manually:

let swiftDisposable: Disposable
let objcDisposable = RACDisposable {
    swiftDisposable.dispose()
}