如何在Swift泛型数据结构(协议类型)中使用弱引用?

本文介绍了如何在Swift泛型数据结构(协议类型)中使用弱引用?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我想在通用数据结构中使用弱引用；在里面 数组下面的示例，但通常是任何泛型类型.我几乎可以得到它 工作:(

I am wanting to use weak references in generic data structures; in the example below an Array, but in general any generic type. I can almost get it to work :(

我的实验进展顺利；以下作品:

My experiments started off well; the following works:

// Array of weak references OK struct WeakReference<T: AnyObject> { weak var value: T? } class C { var i: Int = 0 } let c = C() // Strong reference to prevent collection let weakCs = [WeakReference(value: c)] // OK print("C: \(weakCs[0].value!.i)") // 0

我可以添加一个协议:

// Array of weak references that implements a protocol OK protocol P: AnyObject { // Note AnyObject var i: Int { get } } class CP: P { var i: Int = 0 } let cP = CP() // Strong reference to prevent collection let weakCPs = [WeakReference(value: cP)] // OK print("CP: \(weakCPs[0].value!.i)") // 0

但是当我想要对协议的一系列弱引用时，我得到一个错误:

But when I want an array of weak references to the protocol I get an error:

// Array of weak references of a protocol not OK let weakPs: [WeakReference<P>] = [WeakReference(value: cP)] // Using 'P' as a concrete type conforming to protocol 'AnyObject' is not supported print("P: \(weakPs[0].value!.i)") // 0

有什么我想念的吗?

错误消息使用'P'作为符合协议的具体类型 不支持"AnyObject""，表示这是对的临时限制 编译器.这会解决吗?我应该提交错误报告吗?

The error message, "Using 'P' as a concrete type conforming to protocol 'AnyObject' is not supported", implies that it is a temporary limitation of the compiler. Is this going to be fixed? Should I lodge a bug report?

预先感谢您的任何建议，

Thanks in advance for any advice,

-霍华德.

推荐答案

我在玩耍时发现:

// Array of weak references of a protocol OK so long as protocol marked @objc @objc protocol P { // Note @objc var i: Int { get } } class CP: P { var i: Int = 0 } let weakPs: [WeakReference<P>] = [WeakReference(value: cP)] // Note typed as `[WeakReference<P>]` print("P: \(weakPs[0].value!.i)") // 0

有效:)

令人讨厌的是，您必须使用@objc，因此不能使用纯粹的Swift解决方案，但是由于我在iOS上使用，这对我来说不是问题.

It is annoying that you have to use @objc and therefore not a pure Swift solution, but since I am on iOS not a problem for me.