其中 Self: UIViewcontroller ->编译器认为我正在处理一个非 AnyObject 实例 [英] where Self: UIViewcontroller -> Compiler thinks I am dealing with a non-AnyObject instance

问题描述

这是我的代码

public protocol MyProtocol where Self: UIViewController {
    var money: Int { get set }
}

public extension MyProtocol {
    func giveMoney() { // <-- ERROR: Left side of mutating operator isn't mutable: 'self' is immutable
        money += 1
    }
}

这个错误不应该被抛出吧?该协议的每个符合实例都是一个 UIViewController，因此是 AnyObject 的子类.编译器验证这一点，因为当我将 : AnyObject 添加到我的协议时，它会编译.但是:现在我看到一个丑陋的错误:

This error shouldn't be thrown right? Every conforming instance of this protocol is a UIViewController, therefore a subclass of AnyObject. The compiler validates this, because when I add : AnyObject to my protocol, it compiles. BUT: Now I see an ugly error:

冗余约束 'Self' : 'AnyObject'

Redundant constraint 'Self' : 'AnyObject'

这是编译代码(因此带有编译器警告):

This is the compiling code (so with the compiler warning):

public protocol MyProtocol: AnyObject where Self: UIViewController {
    var money: Int { get set }
}

public extension MyProtocol {
    func giveMoney() {
        money += 1
    }
}

这是bug吗?我使用的是 Xcode 10 和 Swift 4.2.

Is this some bug? I am using Xcode 10 and Swift 4.2.

推荐答案

问题是不支持这个语法:

The problem is that this syntax is not supported:

public protocol MyProtocol where Self: UIViewController {

它可以编译，有点，但这个事实是一个错误.正确的语法是将 where 条件附加到扩展名:

It compiles, sort of, but that fact is a bug. The correct syntax is to attach the where condition to the extension:

public protocol MyProtocol  {
    var money: Int { get set }
}
public extension MyProtocol where Self: UIViewController {
    func giveMoney() { 
        money += 1
    }
}

这篇关于其中 Self: UIViewcontroller ->编译器认为我正在处理一个非 AnyObject 实例的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！