swift - 面向协议(protocol)编程: General struct of type Any in Protocol + introspection valueForKey()

Question

当为 Any 类型的结构设置协议(protocol)时，我希望可以将结构的类型设置为我想要的类型。以下代码是从我制作的 Playground 粘贴的:

import Foundation

// MyStruct does not conform to protocol StructProtocol
// With a general type for struct, like Any, AnyStruct or just Struct, this should be possible
struct MyStruct: StructProtocol {
  var thisStruct: ThisStruct
  var thatStruct: ThatStruct
}

struct ThisStruct {
  var someString: String
}

struct ThatStruct {
  var someOtherString: String
  var andAnotherString: String
}

protocol StructProtocol {
  // Should be able to put Any / AnyStruct / Struct here for a generic struct
  var thisStruct: Any {get}
  var thatStruct: Any {get}
}

extension StructProtocol {
  func saySomething() {
    let firstMirror = Mirror(reflecting: self.thisStruct)
    let secondMirror = Mirror(reflecting: self.thatStruct)

    for structVar in firstMirror.children {
      print(self.thisStruct.valueForKey(structVar))
    }

    for structVar in secondMirror.children {
      print(self.thatStruct.valueForKey(structVar))
    }
  }
}

var thisStruct = ThisStruct(someString: "Hi")
var thatStruct = ThatStruct(someOtherString: "Hello", andAnotherString: "Hola")

var myStruct = MyStruct(thisStruct: thisStruct, thatStruct: thatStruct)
myStuct.saySomething()

// Should output "Hi", "Hello" and "Hola"

目前，协议(protocol)没有可以引用的通用结构类型。必须将结构变量设置为与协议(protocol)完全相同的类型。也许我误解了这一点，并且有一种方法可以实现我正在寻找的东西，但到目前为止我还没有找到答案。

我认为在 Swift 中做到这一点会很棒，所以如果没有办法实现这一点，我会将其作为 Swift 项目中的功能请求发布，但首先我将由各位专家在 StackOverflow 中运行它。

所以问题是:这是否可以通过其他方式实现？

Answer 1

您可以使用多种协议(protocol)执行您所描述的操作。您所要求的问题是如何使用这些通用结构(如果它们不符合其他协议(protocol)或采用一些通用参数) - 您必须对它们进行强制转换，然后通用的全部要点你所要求的自然已经失去了。

所以，你可以这样做:

protocol InnerProtocol {
    func printChildren()
}

protocol StructProtocol {
    var inner1: InnerProtocol {get}
    var inner2: InnerProtocol {get}
}


struct MyStruct : StructProtocol {
    var inner1: InnerProtocol
    var inner2: InnerProtocol
}

struct ThisStruct : InnerProtocol {
    var someString: String

    func printChildren() {
        print(someString)
    }
}

struct ThatStruct : InnerProtocol {
    var someOtherString: String
    var andAnotherString: String

    func printChildren() {
        print(someOtherString)
        print(andAnotherString)
    }
}

extension StructProtocol {

    func saySomething() {
        inner1.printChildren()
        inner2.printChildren()
    }
}


var thisStruct = ThisStruct(someString: "Hi")
var thatStruct = ThatStruct(someOtherString: "Hello", andAnotherString: "Hola")

var myStruct = MyStruct(inner1: thisStruct, inner2: thatStruct)
myStruct.saySomething()