如何声明一个符合协议的特定类的属性？ [英] How to declare a property of a particular class which is also protocol conformant?

问题描述

假设我想创建一个属性，它是UIViewController的子类，并且符合协议MyDelegateProtocol。在Objective-C中，我会写如下：

Suppose I want to create a property which is a subclass of UIViewController and also conformant to the protocol MyDelegateProtocol. In Objective-C I would write something like:

@property (strong, nonatomic) UIViewController<MyDelegateProtocol> *delegate;

但是，我不知道如何在Swift中写这个。我知道如何声明一个符合协议的属性，或者一个特定类型的属性：

However, I'm not sure how to write this in Swift. I know how to declare a property which is protocol-conformant, or a property which is of a particular type:

let delegate : MyDelegateProtocol?
let delegate : UIViewController?

但我无法弄清楚如何做到这两点。如果我尝试这样的事情：

But I can't quite figure out how to make it do both. If I try something like:

let delegate : UIViewController<MyDelegateProtocol> ?

然后我得到一个关于的编译器错误不能专门化非泛型类型'UIViewController 。可能是因为我现在正在徘徊于仿制药的土地上。我已经尝试查阅Swift关于协议的协议和其他Stack Overflow问题的书，但我还没有找到我正在寻找的东西。

Then I get a compiler error about Cannot specialize non-generic type 'UIViewController'. Probably because I'm wandering into the land of generics now. I've tried looking through the Swift book on protocols and other Stack Overflow questions regarding protocols, but I haven't found quite what I'm looking for.

推荐答案

3年后回答我自己的问题，Swift 4支持组合类和协议类型：

Answering my own question 3 years later, Swift 4 supports combined class and protocol types:

let delegate: UIViewController & MyDelegateProtocol

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