swift - 在另一个协议(protocol)中重用协议(protocol)中的关联类型

Question

这是我的代码:

protocol Requester {
    associatedtype requestType

    var response: ((requestType) -> ())? { get set }
}

protocol RequestProcesser: AnyObject {
    // Is it possible to define a associated type that is equal to the associated type of Requester?
    associatedtype requester: Requester

    // This associatedtype should always be equal to Requester.requestType
    associatedtype requestType

    var request: requester { get set }
}

extension RequestProcesser {
    func process() {
        request.response = { response in

            // Now I need to cast...
            // Is there any way around this?
            // the type of the response should be equal to requestType so the cast can be omitted right?
            let x = response as! requestType
        }
    }
}

正如您在代码中的注释中看到的那样，我想知道我是否可以约束关联类型，使其与另一个协议(protocol)中的其他关联类型相等。目标是省略类型转换。现在，实现类可以为 requestType 选择不同的类型，这将导致崩溃。

Answer 1

requestType RequestProcessor 中不需要关联类型协议(protocol)，因为它是基于 requester 的隐式协议(protocol)关联类型。

您应该能够定义 RequestProcessor像这样的协议(protocol):

protocol RequestProcesser: AnyObject {
    associatedtype requester: Requester
    var request: requester { get set }
}

然后像这样使用它:

class MyRequester: Requester {
    typealias requestType = Int
    var response: ((Int) -> ())?
}

class MyRequestProcessor: RequestProcesser {
    typealias requester = MyRequester
    var request = MyRequester()
} 

现在，response process() 中的闭包参数方法将采用 MyRequester 的关联类型协议(protocol)(在本例中为 Int )，因此无需转换。