更新关闭到Swift 3 - @escaping [英] Updating closures to Swift 3 - @escaping

问题描述

我已经更新我的代码到Xcode 8.0 beta 6，但我被困住似乎是关于新的非转义闭包默认。在下面的代码中，Xcode建议在 completion：前添加 @escaping 但仍然不会编译和循环。 （ EDIT ：实际上，Xcode建议在之后 完成后添加@escaping。该提醒仍可能显示，但清理和编译将删除它。）该代码如何重写/修正在更新的Swift 3中工作？
我看了新的手册，但我找不到正确的代码示例。

  func doSomething （withParameter参数：Int，completion：（） - >（））{
 //有东西
 
 callSomeOtherFunc（withCompletion：completion）
} 
 
 //调用方法并执行闭包
 doSomething（withParameter：2）{
 //在闭包中执行操作
} 
  
解决方案
 
 Swift 3：closure参数属性现在应用于参数 type ，而不是参数本身
 
 
 
在Swift 3之前，closure属性 @autoclosure 和 @noescape 用于属性的参数，但现在属于参数类型;请参阅以下接受的Swift进展计划：
 
 
 
 
 
 SE-0049：将@noescape和@autoclosure移动为类型属性 
 
 
 
 
 
您的特定问题涉及参数类型属性 @escaping （适用相同的新规则），如接受的Swift演进提议默认情况下允许闭包参数为非转义：
 
 
 
 
 
  SE-0103：将非转义关闭设为默认 
 
 
 
 
 
这些提案现在都在Xcode 8的测试阶段实施（请参见有关Xcode的发行说明8 beta 6 ;需要访问的开发人员帐户登录）
 
 
   Xcode 8 beta 6 -  Swift编译器：Swift语言 
 
 
 
默认情况下，关闭参数不转义，而不是显式
注释为 @noescape 。使用 @escaping 来表示
闭包参数可能会转义。  @autoclosure（escaping）现在写为
  @autoclosure @escaping 。已弃用注释 @noescape 和
  @autoclosure（转义）。 （SE-0103）
 
 
 
 ... 
 
 
 
  Swift和Apple LLVM编译器：Swift语言  
 
 
 
  @noescape  c $ c> @autoclosure 属性现在必须在参数类型之前写入
，而不是在参数名称之前。 [SE-0049] 
 
 
因此，您使用非默认 @escaping 属性如下;应用于闭包参数的类型，而不是参数本身。
  func doSomething ：Int，completion：@escaping（） - >（））{
 // ... 
} 
  
 
 
 
 
 
 
      / p> 
 
 
 
 
 @CristiBăluţă：escape是什么？从来没有看到这个关键字
 before swift3 auto-conversion ... p> 
 
参见eg指向上述 SE-0103演进提案的链接（以及来自beta 6发行说明的引用文本）：以前，闭包参数默认转义（因此不需要存在转义的显式注释），但默认情况下现在改为非转义。因此，添加 @escaping 以显式地注释闭包参数可能会逃脱（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）。 
 
 
 
为了解释一个闭包参数是如何转义的，我引用语言参考 - 属性：
 
 
 应用此属性到一个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用于
以后的执行，这意味着该值允许超过调用的
生存期。 
 
 
 
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: 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
}
Any help much appreciated!
解决方案
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: Move @noescape and @autoclosure to be type attributes


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: Make non-escaping closures the default


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)

  
New in Xcode 8 beta 6 - Swift Compiler: Swift Language
  
  
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)
  
  
...
  
  
New in Xcode 8 beta – Swift and Apple LLVM Compilers: Swift Language
  
  
The @noescape and @autoclosure attributes must now be written 
  before the parameter type instead of before the parameter name. [SE-0049]
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 () -> ()) {
    // ...
}




(Including my answer to a question in an upvoted comment below, as comments are not persistent data on SO)

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

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

  
"Apply this attribute to a parameter’s type in a method or function declaration to indicate that the parameter’s value can be stored for
  later execution. This means that the value is allowed to outlive the
  lifetime of the call."


                        
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