将闭包更新为 Swift 3 - @escaping [英] Updating closures to Swift 3 - @escaping

问题描述

我已将我的代码更新到 Xcode 8.0 beta 6，但我被困在似乎是关于新的非转义闭包默认值的问题上.在下面的代码中，Xcode 建议在下面代码的第一行中的 completion: 前面添加 @escaping ，但这仍然不会编译并循环.*

I've updated my code to Xcode 8.0 beta 6 but I got stuck with what seems to be about the new non escaping closure default. In the following code Xcode suggests to add @escaping in front of completion: in the first line of the below code, but that still won't compile and goes in circles. *

(EDIT:实际上，@escaping 应该添加在 after completion: 中，正如 Xcode 建议的那样.警报可能仍然显示，但清理和编译将删除它.)* 应如何重写/修复此代码以在更新的 Swift 3 中工作?我查看了新手册，但找不到合适的代码示例.

(EDIT: In fact, @escaping should be added in after completion:, as Xcode suggests. The alert may still show but cleaning and compiling will remove it.)* How should this code be re-written / fixed to work in the updated Swift 3? I've had a look in the new manual but I couldn't find proper code samples.

func doSomething(withParameter parameter: Int, completion: () -> ()) {
    // Does something

    callSomeOtherFunc(withCompletion: completion)
  }

// Calling the method and execute closure 
doSomething(withParameter: 2) {
  // do things in closure
}

非常感谢任何帮助！

推荐答案

Swift 3:闭包参数属性现在应用于参数type，而不是参数本身

在 Swift 3 之前，闭包属性 @autoclosure 和 @noescape 曾经是闭包的属性参数，但现在是属性到参数type；请参阅以下已接受的 Swift 进化提案:

Swift 3: closure parameter attributes are now applied to the parameter type, and not the parameter itself

Prior to Swift 3, the closure attributes @autoclosure and @noescape used to be attributes to the closure parameter, but are now attributes to the parameter type; see the following accepted Swift evolution proposal:

• SE-0049:移动@noescape 和@自动关闭是类型属性

您的具体问题与参数类型属性 @escaping(适用相同的新规则)有关，如已接受的 Swift 进化提案中所述，默认情况下让闭包参数不转义:

Your specific question pertain to parameter type attribute @escaping (for which the same new rule applies), as described in the accepted Swift evolution proposal to let closure parameters be non-escaping by default:

• SE-0103:将非转义闭包设为默认值

这些提议现在都在 Xcode 8 的 beta 阶段实施(请参阅 Xcode 8 beta 6 的发行说明; 访问需要开发帐户登录)

These proposals are now both implemented in the beta stage of Xcode 8 (see release notes for Xcode 8 beta 6; dev. account login needed for access)

Xcode 8 beta 6 的新功能 - Swift 编译器:Swift 语言

闭包参数默认是非转义的，而不是明确的使用 @noescape 进行注释.使用 @escaping 表示一个关闭参数可能会转义.@autoclosure(escaping) 现在写成@autoclosure @escaping.注释 @noescape 和@autoclosure(escaping) 已弃用.(SE-0103)

Closure parameters are non-escaping by default, rather than explicitly being annotated with @noescape. Use @escaping to indicate that a closure parameter may escape. @autoclosure(escaping) is now written as @autoclosure @escaping. The annotations @noescape and @autoclosure(escaping) are deprecated. (SE-0103)

...

Xcode 8 beta 中的新功能 – Swift 和 Apple LLVM 编译器:Swift 语言

@noescape 和 @autoclosure 属性现在必须写入在参数类型之前而不是在参数名称之前.[SE-0049]

The @noescape and @autoclosure attributes must now be written before the parameter type instead of before the parameter name. [SE-0049]

因此，您使用非默认的 @escaping 属性如下；应用于闭包参数的类型，而不是参数本身

Hence, you use the non-default @escaping attribute as follows; applied to the type of the closure parameter, rather than the parameter itself

func doSomething(withParameter parameter: Int, completion: @escaping () -> ()) {
    // ...
}

<小时>

(包括我在下面一个点赞评论中对问题的回答，因为评论不是关于 SO 的持久数据)

@Cristi Băluță:逃避有什么作用?从未见过这个关键词在 swift3 自动转换之前......

@Cristi Băluță: "What does escaping do? Never seen this keywords before swift3 auto-conversion ... "

参见例如上述SE-0103进化提案的链接(以及 beta 6 发行说明中引用的文本):以前，闭包参数默认情况下会转义(因此不需要存在用于转义的显式注释)，但现在默认情况下是非转义的.因此，添加 @escaping 以明确注释闭包参数可能会转义(与其默认行为相反).这也解释了为什么 @noescape 现在已被弃用(无需注释默认行为).

See e.g. the link to the SE-0103 evolution proposal above (as well as the quoted text from the beta 6 release notes): previously, closure parameters were escaping by default (hence no need for the existence of an explicit annotation for escaping), but are now instead non-escaping, by default. Hence the addition of @escaping to explicitly annotate that a closure parameter may escape (contrary to its default behaviour). This also explains why @noescape is now deprecated (no need to annotate the default behaviour).

为了解释闭包参数转义的含义，我引用了 语言参考 - 属性:

For explaining what it means that a closure parameter is escaping, I quote the Language Reference - attributes:

"将此属性应用于方法或函数声明中的参数类型，以指示该参数的值可以存储为后来执行.这意味着允许该值比调用的生命周期."

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