协议扩展，变异功能 [英] Protocol Extension, Mutating Function

问题描述

我正在使用swift 2.0，我在协议上有一个协议和一个扩展来创建一个方法的默认实现，代码是休闲：

I am using swift 2.0, I have a protocol and an extension on the protocol to create a default implementation of a method, the code is as fallows:

protocol ColorImpressionableProtocol {

    var lightAccentColor: UIColor? {get set}
    var accentColor: UIColor? {get set}
    var darkAccentColor: UIColor? {get set}
    var specialTextColor: UIColor? {get set}

    mutating func adoptColorsFromImpresion(impresion: ColorImpressionableProtocol?)
}

extension ColorImpressionableProtocol {

    mutating func adoptColorsFromImpresion(impresion: ColorImpressionableProtocol?){
        lightAccentColor = impresion?.lightAccentColor
        accentColor = impresion?.accentColor
        darkAccentColor = impresion?.darkAccentColor
        specialTextColor = impresion?.specialTextColor
    }
}

我稍后在我的代码中尝试调用此方法并获得了错误如下：

I am later on in my code trying to call this method and am getting an error that reads:

不能在不可变值上使用变异成员：'self'是不可变的

"cannot use mutating member on immutable value:'self' is immutable"

代码是休闲：

init(impresion: ColorImpressionableProtocol?){
        super.init(nibName: nil, bundle: nil)
        adoptColorsFromImpresion(impresion)
}

我唯一可以做的事情认为在这种情况下，'Self'是一个协议，而不是一个类。但是我必须遗漏一些使这个概念起作用的东西，一个由协议定义的方法的默认实现，该协议编辑同样协议定义的值。

The only thing I can think of is that 'Self' in this case is a protocol, not a class. However I have to be missing something to make this concept work, A default implementation of a method defined by a protocol that edits values also defined by the same protocol.

谢谢为了你的帮助和时间：）

Thank you for your help and time :)

推荐答案

如果你打算只为课程使用协议，你可以赚
它是类协议（并删除变异关键字）：

If you intend to use the protocol only for classes then you can make it a class protocol (and remove the mutating keyword):

protocol ColorImpressionableProtocol : class {

    // ...

    func adoptColorsFromImpresion(impresion: ColorImpressionableProtocol?)
}

然后

init(impresion: ColorImpressionableProtocol?){
    super.init(nibName: nil, bundle: nil)
    adoptColorsFromImpresion(impresion)
}

编译没有问题。

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