“Protocol ...只能用作通用约束，因为它具有Self或相关类型要求”意思？ [英] What does "Protocol ... can only be used as a generic constraint because it has Self or associated type requirements" mean?

问题描述

我正在尝试创建一个字典（实际上是一个 HashSet ），并将其键入一个自定义协议在Swift中，但它给了我标题中的错误：

lockquote
协议'myProtocol'只能用作通用约束，因为它有自我或相关类型的要求

我无法正面或反面。

  protocol观察：Hashable {} 
 
 var observers = HashSet< Observing>（）
  

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更新：

为什么这是查看此视频的方式。

$ b $协议观察从协议继承 Hashable ，它继而从协议<继承code> Equatable 。 Protocol Equatable 具有以下要求：

  func ==（lhs： Self，rhs：Self） - > Bool 
  

一个包含 Self 某处的协议里面它不能在任何地方使用，除非在类型约束中。

这里是一个类似的问题。

I am trying to create a Dictionary (actually a HashSet) keyed on a custom protocol in Swift, but it is giving me the error in the title:

Protocol 'myProtocol' can only be used as a generic constraint because it has Self or associated type requirements

and I can't make heads nor tails of it.

protocol Observing: Hashable { }

var observers = HashSet<Observing>()

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Update:

For the best possible explanation for why this is the way it is check out this video.

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解决方案

Protocol Observing inherits from protocol Hashable, which in turn inherits from protocol Equatable. Protocol Equatable has the following requirement:

func ==(lhs: Self, rhs: Self) -> Bool

And a protocol that contains Self somewhere inside it cannot be used anywhere except in a type constraint.

Here is a similar question.

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