与 struct 中定义的 Void 回调相关的 Swift 编译器错误的解决方法/解决方案 [英] Workaround/resolution for Swift compiler error related to Void callback defined in struct

问题描述

由于 Swift 中 typealias 定义缺乏通用支持，我编写了一个通用的 ResultHandler 回调，如下所示:

Due to the lack of generic support in typealias definitions in Swift, I wrote a generic ResultHandler<T> callback like so:

struct ResultHandler<T> {
    let f: (result: T) -> ()
}

这对于使用 Void 以外的任何东西的处理程序非常有用:

This works great for handlers that use anything other than Void:

Dispatch<Bool>.dispatch({ () -> (Result<Bool>) in
    Result<Bool>(true)
}).onResult(ResultHandler() { (result: Bool) in
    if result {
        self.doSomething() // Method executes successfully
    }
})

但是当尝试使用 Void 时:

But when attempting to use Void:

Dispatch<Void>.dispatch({ () -> (Result<Void>) in
    Result<Void>()
}).onResult(ResultHandler() { (result: Void) in // Compiler error here
    self.doSomething()
})

存在编译错误:

函数签名'(Void) -> ()' 与预期类型不兼容'(结果:无效)-> ()'

Function signature '(Void) -> ()' is not compatible with expected type '(result: Void) -> ()'

这似乎误导/编译器错误，好像我更改了签名以使用错误类型的值:

Which seems misleading/a compiler bug, as if I change the signature to use a wrongly-typed value:

Dispatch<Void>.dispatch({ () -> (Result<Void>) in
    Result<Void>()
}).onResult(ResultHandler() { (result: Void?) in // Compiler error here
    self.doSomething()
})

错误消息选择了可选的指示 ?，但仍然没有正确检测到我的 result: 标签:

The error message picks up the optional-indicating ?, but still does not properly detect my result: label:

函数签名'(Void?) -> ()' 与预期类型不兼容'(结果:无效)-> ()'

Function signature '(Void?) -> ()' is not compatible with expected type '(result: Void) -> ()'

我做错了什么?

推荐答案

您不需要在闭包类型声明中指定参数名称——这就是编译器出现问题的原因:

You don't need to specify parameter names in closure type declarations—that's what's giving the compiler problems:

struct ResultHandler<T> {
    let f: T -> ()
}

现在您可以创建使用 Bool 参数、Void 参数或完全省略参数的 ResultHandler 实例:

Now you can create ResultHandler instances that use a Bool parameter, a Void parameter, or leave out the parameter altogether:

let r1 = ResultHandler() { (result: Bool) in
    if result {
        // do something
    }
}

let r2 = ResultHandler() { (_: Void) in
    // do something
}

let r3 = ResultHandler() {
    // do something
}

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