Swift 1.0: missing argument label 'xxx' in call

注意，这个问题是在swift1.0时发生的，swift2.0中，好像统一了function 和 method 的定义，具体待正式版发布后研究一下！

 

今天在使用swift时发现，写的func老是要求写出第二个参数的外部变量名，很不理解，感受和书上说的function不同，查了一下，终于发现了缘由：写在class内部的function叫作method，是特殊的functoin，系统会自动补上外部变量名，参看如下链接 http://stackoverflow.com/questions/24050844/swift-missing-argument-label-xxx-in-call

 

防止链接失效，截取部份内容以下：

One possible reason is that it is actually a method. Methods are very sneaky, they look just like regular functions, but they don't act the same way, let's look at this:

func funFunction(someArg: Int, someOtherArg: Int) {
    println("funFunction: \(someArg) : \(someOtherArg)")
}

// No external parameter
funFunction(1, 4)

func externalParamFunction(externalOne internalOne: Int, externalTwo internalTwo: Int) {
    println("externalParamFunction: \(internalOne) : \(internalTwo)")
}

// Requires external parameters
externalParamFunction(externalOne: 1, externalTwo: 4)

func externalInternalShared(#paramOne: Int, #paramTwo: Int) {
    println("externalInternalShared: \(paramOne) : \(paramTwo)")
}

// The '#' basically says, you want your internal and external names to be the same

externalInternalShared(paramOne: 1, paramTwo: 4)

Now here's the fun part, declare a function inside of a class and it's no longer a function ... it's a method

class SomeClass {
    func someClassFunctionWithParamOne(paramOne: Int, paramTwo: Int) {
        println("someClassFunction: \(paramOne) : \(paramTwo)")
    }
}

var someInstance = SomeClass()
someInstance.someClassFunctionWithParamOne(1, paramTwo: 4)

This is part of the design of behavior for methods

Apple Docs:

Specifically, Swift gives the first parameter name in a method a local parameter name by default, and gives the second and subsequent parameter names both local and external parameter names by default. This convention matches the typical naming and calling convention you will be familiar with from writing Objective-C methods, and makes for expressive method calls without the need to qualify your parameter names.