Transitionable

public protocol Transitionable

The “state” part of our finite state machine.

Instances of the conforming type model the states of our system. Their implementations of shouldTrasition(to:) determine what transitions between states are allowed.

Note

In theory, this could be any type capable of calculating whether a transition between two instances of itself are legal. In practice, it’s almost always best to use an enum. For example:

enum TrafficLight: Transitionable {
  case red, yellow, green

  func shouldTransition(to: Self) -> Bool {
    switch (self, to) {
    case (.red, green),
         (.green, .yellow),
         (.yellow, red):
      return true
    default:
      return false
    }
  }
}

  • Defines whether a transition from self to the given state is valid.

    Declaration

    Swift

    func shouldTransition(to: Self) -> Bool

    Parameters

    to

    The type to potentially transition to.

    Return Value

    true if it’s legal to trasition from self to to. Otherwise, false.