ShouldEmitValue

public enum ShouldEmitValue<StateType>

A predicate that determines if a state change should notify subscribers or not, by comparing previous and new states and returning a Bool true in case it should emit it, or false in case it should not emit it. It comes with some standard options like .always, .never, .when(old, new) -> Bool and, for Equatable structures, .whenDifferent.

  • It will always emit changes, regardless of previous and new state

    Declaration

    Swift

    case always

  • It will never emit changes, regardless of previous and new state

    Declaration

    Swift

    case never

  • It’s a custom-defined predicate, you’ll be given old and new state, and must return a Bool indicating what you’ve decided from that change, being true when you want this change to be notified, or false when you want it to be ignored.

    Declaration

    Swift

    case when((StateType, StateType) -> Bool)

  • Evaluates the predicate and returns true in case this should be emitted, or false in case this change should be ignored

    Declaration

    Swift

    public func shouldEmit(previous: StateType, new: StateType) -> Bool

  • Evaluates the predicate and returns true in case this should be ignored, or false in case this change should be emitted. It’s the exact inversion of shouldEmit and useful for operator .removeDuplicates that some Reactive libraries offer.

    Declaration

    Swift

    public func shouldRemove(previous: StateType, new: StateType) -> Bool

Available where StateType: Equatable

  • For Equatable structures, .whenDifferent will run == operator between old and new state, and notify when they are different, or ignore when they are equal.

    Declaration

    Swift

    public static var whenDifferent: ShouldEmitValue<StateType> { get }