在Swift 3.0中转义self（struct / enum）内部转义 [英] Mutating self (struct/enum) inside escaping closure in Swift 3.0

问题描述

在swift 2.2中，当它在一个变异函数中时，我们可以在一个闭包中变异一个struct或enum。但在swift 3.0中它不再可能。我收到以下错误

In swift 2.2, We could mutate a struct or enum within a closure, when it was inside a mutating function. But in swift 3.0 its no longer possible. I get the following error

闭包不能隐式捕获变异的自我参数

closure cannot implicitly captured a mutating self parameter

这是一段代码片段，

struct Point {
    var x = 0.0, y = 0.0

    mutating func moveBy(x deltaX: Double, y deltaY: Double) {
        x += deltaX
        y += deltaY

        test { (a) -> Void in
            // Get the Error in the below line.
            self.x = Double(a)
        }

    }

    mutating func test(myClosure: @escaping (_ a: Double) -> Void) {
        myClosure(3)
    }
}

我得到的值类型不应该是可变的。我有一些情况，当我收到API响应时，我必须在其中一个函数中修改结构中的一个变量。 （在完成结束时）

I get that value types are not supposed to be mutable. I have cases, where I do have to modify one variable in the struct within one of the functions, when I receive the API response. (In the completion closure)

我在swift 2.2中做了什么，不可能或者有没有办法实现这个目标？

Is what I was doing in swift 2.2, impossible or is there way to accomplish this?

推荐答案

问题是 @escaping闭包可以存储以供以后执行：

逃离关闭

当闭包作为参数传递给函数时，闭包被称为转义函数，但在函数返回后调用。 ...

A closure is said to escape a function when the closure is passed as an argument to the function, but is called after the function returns. ...

闭包可以转义的一种方法是存储在函数外部定义的变量....

One way that a closure can escape is by being stored in a variable that is defined outside the function....

由于闭包可以存储并存在于函数范围之外，因此闭包内的struct / enum（self）将被复制（它是一个值）闭包的参数。并且，如果它被允许变异，那么关闭可能会有一个旧的副本，导致不必要的结果。

Since the closure can be stored and live outside the scope of the function, the struct/enum inside the closure (self) will be copied (it is a value) as a parameter of the closure. And, if it was allowed to mutate, the closure could have an old copy of it, causing unwanted results.

所以，回答你的问题，你不能;除非你能删除@escaping（不是你的情况，因为它是第三方API）

So, in answer to your question, you cannot; unless you are able to remove "@escaping" (not your case because it's a 3rd party API)

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