ReactiveSwift and ReactiveCocoa extensions and utilities.
These guidelines aim at improving consistency and intuitiveness of reactive API design.
While ReactiveSwift and ReactiveCocoa tend to use past sense for naming signal events, like Life.ended or Action.completed, Apple prefers emphatic form, like NSView.didHide or AVCaptureSessionDidStartRunning, complimented by auxiliary verbs (will, did, was). Moreover, Swift also uses emphatic form in the language itself, like willSet and didSet property observers, so it's safe to assume that this is the overall convention at Apple. Hence, events should use emphatic naming form with auxiliary verbs and follow established Apple's convention as closely as possible.
extension Reactive {
var willAppear: Signal<…>
var didAppear: Signal<…>
}