swift – 类不符合协议.为什么？

class Controller<U: NSObject> {}

protocol Robert {
  associatedtype T
  associatedtype U: Controller<T>
  var fetcher: U { get }
}

class Telephone: NSObject {}

class Object: Telephone {}

class Turtle: Controller<Object> {}

class Fish: Robert {

  typealias T = Object
  typealias U = Turtle

  let x = Turtle()

  var fetcher: Turtle {
    return x
  }

}

我不明白为什么.任何帮助赞赏.

选择XCode“修复它”选项时,会插入“Fetcher”的存根.但是Fetcher已经有了一个类型.

所以这并不酷

associatedtype U: Controller<T>

删除它会产生以下结果,这是有效的.

protocol Robert {
  associatedtype T: NSObject
  var fetcher: Controller<T> { get }
}