斯威夫特5。协议扩展引发编译错误 'Cannot invoke function with an argument list of type Self'

Question

我想实现某种 Decorator 模式，它允许编写 可重用装饰器

所以我定义了2个协议。第一个定义装饰器的类型：

    protocol ViewDecorator {
        associatedtype View: Decoratable
        func decorate(view: View)
    }

    // this is how I expect to use decorator
    class GreenViewDecorator: ViewDecorator {
        typealias View = GreenView

        func decorate(view: GreenView) {
            view.backgroundColor = UIColor.green
        }
    }

第二个定义 decoratable 视图应符合的类型。

    protocol Decoratable {
        func decorate<T: ViewDecorator>(with decorator: T)
    }

    extension Decoratable where Self: UIView {
        func decorate<T : ViewDecorator>(with decorator: T) {
            decorator.decorate(view: self)
        }
    }

    // exampled of 'decoratable' view
    class GreenView: UIView, Decoratable { }

我在协议扩展中定义了函数 func decorate<T : ViewDecorator>(with decorator: T) 的默认实现。我发现如果我的视图默认实现该方法是很有用的。我只需要它只继承 Decoratable 协议。然后我可以像这样使用它：

    // example of using decorator with view
    let decorator = GreenViewDecorator()
    greenView.decorate(with: decorator)

但是 Swift5 编译器在 decorator.decorate(view: self)

行引发错误

Cannot invoke 'decorate' with an argument list of type '(view: Self)'

============== TOTAL LISTING ==========
    protocol ViewDecorator {
        associatedtype View: Decoratable
        func decorate(view: View)
    }

    protocol Decoratable {
        func decorate<T: ViewDecorator>(with decorator: T)
    }

    extension Decoratable where Self: UIView {
        func decorate<T : ViewDecorator>(with decorator: T) {
            decorator.decorate(view: self)
        }
    }

    class GreenView: UIView, Decoratable { }

    class GreenViewDecorator: ViewDecorator {
        typealias View = GreenView

        func decorate(view: GreenView) {
            view.backgroundColor = UIColor.green
        }
    }

    class ViewController: UIViewController {
        @IBOutlet var greenView: GreenView!

        override func viewDidLoad() {
            super.viewDidLoad()
            let decorator = GreenViewDecorator()
            greenView.decorate(with: decorator)
        }
    }

Answer 1

参数的类型是关联类型 View，但尚未确定 Self 是那种类型，因此您不能传递类型 Self 的参数没有确定它是兼容的。例如：

extension Decoratable where Self: UIView {
    func decorate<T: ViewDecorator>(with decorator: T) where T.View == Self {
        decorator.decorate(view: self)
    }
}

（但是，如果你这样做，你将难以遵守 Decoratable 协议，因为它需要此方法用于 any ViewDecorator。你可以更改协议也具有相同的 T.View == Self 限制。）

斯威夫特5。协议扩展引发编译错误 'Cannot invoke function with an argument list of type Self'

Swift5. Protocol extension raises compilation error 'Cannot invoke function with an argument list of type Self'

xcode

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associated-types

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