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A Simple Swift State Machine
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| import Foundation | |
| class StateMachine <P: StateMachineDelegateProtocol> { | |
| private unowned let delegate: P | |
| private var _state: P.StateType { | |
| didSet{ | |
| delegate.didTransitionFrom(from: oldValue, to: _state) | |
| } | |
| } | |
| var state: P.StateType { | |
| get{ | |
| return _state | |
| } | |
| set{ | |
| // Can't be an observer because we need the option to CONDITIONALLY set state | |
| delegateTransitionTo(to: newValue) | |
| } | |
| } | |
| init(initialState: P.StateType, delegate: P) { | |
| // Set the primitive to avoid calling the delegate. | |
| _state = initialState | |
| self.delegate = delegate | |
| } | |
| private func delegateTransitionTo(to: P.StateType) { | |
| switch delegate.shouldTransitionFrom(from: _state, to: to) { | |
| case .Continue: | |
| _state = to | |
| case .Redirect(let newState): | |
| _state = to | |
| state = newState | |
| case .Abort: | |
| break; | |
| } | |
| } | |
| } | |
| protocol StateMachineDelegateProtocol: class { | |
| associatedtype StateType | |
| func shouldTransitionFrom(from: StateType, to: StateType) -> Should<StateType> | |
| func didTransitionFrom(from: StateType, to: StateType) | |
| } | |
| enum Should<T> { | |
| case Continue, Abort, Redirect(T) | |
| } |
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| import UIKit | |
| class Example : UIView{ | |
| private var machine:StateMachine<Example>! | |
| enum TrafficLight{ | |
| case Stop, Go, Caution | |
| } | |
| required init(coder aDecoder: NSCoder) { | |
| super.init(coder: aDecoder) | |
| machine = StateMachine(initialState: .Stop, delegate: self) | |
| } | |
| @IBAction func tappedGo(sender:AnyObject){ | |
| machine.state = .Go | |
| } | |
| @IBAction func tappedCaution(sender:AnyObject){ | |
| machine.state = .Caution | |
| } | |
| } | |
| extension Example : StateMachineDelegateProtocol{ | |
| typealias StateType = TrafficLight | |
| func shouldTransitionFrom(from: StateType, to: StateType) -> Should<StateType> { | |
| switch (from, to){ | |
| case (.Stop, .Go), (.Caution, .Stop): | |
| return .Continue | |
| case (.Go, .Caution): | |
| return .Redirect(.Stop) | |
| default: | |
| return .Abort | |
| } | |
| } | |
| func didTransitionFrom(from: StateType, to: StateType) { | |
| switch to{ | |
| case .Stop: | |
| backgroundColor = UIColor.redColor() | |
| case .Go: | |
| backgroundColor = UIColor.greenColor() | |
| case .Caution: | |
| backgroundColor = UIColor.yellowColor() | |
| } | |
| } | |
| } |
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