无效的typealias声明 [英] Invalid redeclaration of typealias

问题描述

我有一个通用协议 TwoWayBindDelegate ，该协议使用通用关联类型来确定函数 twoWayBind()

I have a generic protocol, TwoWayBindDelegate, that uses the generic associated type to determine the parameters of the function twoWayBind()

protocol TwoWayBindDelegate: class {

    associatedtype BindType

    func twoWayBind(to observable: Observable<BindType>?, observableChanged: ((BindType) -> ())?)
}

然后我创建了一个类， Reactive< Base:UIView，Type> (符合 TwoWayBindDelegate )，在其中必须使用通用的 Base对其进行初始化..例如: let reactSlider = Reacive< UISlider>(滑块).

I then created a class, Reactive<Base: UIView, Type> (which conforms to TwoWayBindDelegate) where you have to initialize it with the generic Base. For eg: let reactiveSlider = Reacive<UISlider>(slider).

我的问题是，当我扩展Reactive并符合 TwoWayBindDelegate 时，出现错误 BindType'无效重新声明，因为我声明了 BindType 和 twoWayBind().有没有办法让两个扩展都为 TwoWayBindDelegate

My issue is when I am extending Reactive and conforming to TwoWayBindDelegate, I get an error Invalid redeclaration of 'BindType' because I am declaring BindType and twoWayBind() in both my extensions. Is there a way I can have both extensions provide different implementations for TwoWayBindDelegate

class Reactive<Base: UIView>: TwoWayBindDelegate {

    public var base: Base

    init(base: Base) {
        self.base = base
    }
}

extension Reactive where Base == UISlider {

    typealias BindType = Float        

    func twoWayBind(to observable: Observable<Float>?, observableChanged: ((Float) -> ())?) {
        // implement two way bind for UISlider
    }
}

extension Reactive where Base == UITextField {

    typealias BindType = String        

    func twoWayBind(to observable: Observable<String>?, observableChanged: ((String) -> ())?) {
        // implement two way bind for UITextField
    }
}

我做了一些研究，发现它可能是一个错误 https://bugs.swift.org/browse/SR-5392 .碰巧有解决方法

I did some research and found out that it may be a bug https://bugs.swift.org/browse/SR-5392. Does there happen to be a workaround

推荐答案

我不太明白 typealias 的用途.仅函数声明就足以告诉编译器 BindType 必须是什么.

I don't quite see what the typealias is for. The function declaration alone is sufficient to tell the compiler what BindType must be.

我在您的代码中发现的问题(当然，除了缺少的Observable声明)是Reactive类 itself 不符合TwoWayBindDelegate.为了解决这个问题，我引入了 twoWayBind 的任意实现.当我这样做时，以及当我删除了不必要的 typealias 声明时，您的代码就会为我编译:

The problem I found with your code (apart from the missing Observable declaration, of course) is that the Reactive class itself doesn't conform to TwoWayBindDelegate. To get around that, I threw in an arbitrary implementation of twoWayBind. When I did, and when I deleted the unnecessary typealias declarations, your code compiled for me:

struct Observable<T> {}

protocol TwoWayBindDelegate: class {
    associatedtype BindType
    func twoWayBind(to observable: Observable<BindType>?, observableChanged: ((BindType) -> ())?)
}

class Reactive<Base: UIView>: TwoWayBindDelegate {
    public var base: Base
    init(base: Base) {
        self.base = base
    }
    func twoWayBind(to observable: Observable<Int>?, observableChanged: ((Int) -> ())?) {
    }
}

extension Reactive where Base == UISlider {
    func twoWayBind(to observable: Observable<Float>?, observableChanged: ((Float) -> ())?) {
    }
}

extension Reactive where Base == UITextField {
    func twoWayBind(to observable: Observable<String>?, observableChanged: ((String) -> ())?) {
    }
}

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