Swift 函数，一个参数两个名称

Question

我注意到一些方法，例如init(nibName nibName: String?, bundle nibBundle: NSBundle?) 有两个 "names" 作为一个参数，除了第一个参数不可能在内部方法中使用。在这种情况下，您无法使用 bundle 但可以使用 nibBundle。例如，当我调用 super.init(nibName: nibName, bundle: bundle) 时出现错误 "Use of unresolved identifier 'bundle'".

我的问题是：它（双命名参数）有什么用？如何正确使用？

编辑：现在很明显是外部参数名称。我有 UIViewController 的子类并重写以下方法。我不明白 nibBundle 从哪里来？显然它没有在函数头中定义。

override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: NSBundle?) {
   super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)
   let someBundle = nibBundle
   print(someBundle)
}

Answer 1

名字是 public 名字，第二个是私有的（只能在函数中使用）

Answer 2

来自 Apple 的文档：

Sometimes it’s useful to name each parameter when you call a function, to indicate the purpose of each argument you pass to the function.

If you want users of your function to provide parameter names when they call your function, define an external parameter name for each parameter, in addition to the local parameter name. You write an external parameter name before the local parameter name it supports, separated by a space:
func someFunction(externalParameterName localParameterName: Int) {
    // function body goes here, and can use localParameterName
    // to refer to the argument value for that parameter
}

Shorthand 外部参数名称

If you want to provide an external parameter name for a function parameter, and the local parameter name is already an appropriate name to use, you do not need to write the same name twice for that parameter. Instead, write the name once, and prefix the name with a hash symbol (#). This tells Swift to use that name as both the local parameter name and the external parameter name.

https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Functions.html

Swift 函数，一个参数两个名称

Swift function, two names for one parameter

parameters

function

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