如何使用SWIFT协议与泛型方法和泛型类型

Question

我有一个类StateMachine<A>

final class StateMachine<A> { 

    private var previousState: State? = nil 
    private var currentState: State 
    private var content: A? 
    var delegate: StateMachineDelegate? 
    var state: State = .loading { 
     didSet { 
      previousState = currentState 
      currentState = state 
     } 
    } 

    init(currentState: State, delegate: StateMachineDelegate?) { 
     self.currentState = currentState 
    } 
} 

和委托协议StateMachineDelegate

protocol StateMachineDelegate { 
    func updateWith(content: A) 
} 

我想表达的是，如果创建的StateMachine对于类型A，代表应该实现方法func updateWith(content: A)，它接受一个相同类型A的参数。这可能吗？

Answer 1

你会实现你通过添加其他类型的参数要求的东西：

final class StateMachine<A, Delegate: StateMachineDelegate> where Delegate.A == A { 

    private var previousState: State? = nil 
    private var currentState: State 
    private var content: A? 
    var delegate: Delegate? 
    var state: State = .loading { 
     didSet { 
      previousState = currentState 
      currentState = state 
      delegate?.updateWith(content: state) 
     } 
    } 

    init(currentState: State, delegate: Delegate?) { 
     self.currentState = currentState 
    } 
} 

protocol StateMachineDelegate { 
    associatedtype A 
    func updateWith(content: A) 
} 

但我不会做这种方式。如果您的代理真的只是一个更新的方法，那么闭包是一个更好的解决方案：

final class StateMachine<A> {  
    // ... 
    private var content: A? 
    var notify: (A) -> Void 

    var state: State = .loading { 
     didSet { 
      previousState = currentState 
      currentState = state 
      notify(state) 
     } 
    } 

    init(currentState: State, notify: @escaping (A) -> Void) { 
     self.currentState = currentState 
     self.notify = notify 
    } 
}