ios - Swift : missing argument label 'xxx' in call

Question

func say(name:String, msg:String) {
    println("(name) say (msg)")
}

say("Henry","Hi,Swift")  <---- error because missing argument label 'msg' in call

I need to use

   say("Henry",msg:"Hi,Swift")

Why ? If I put more than two var in func so that I need to write var name instead of first var when I call this func
It's really trouble, and I don't see any explain in iBook Swift tutorial.

Answer 1

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

// Note that there's been an update in Swift 2 and the above function would have to be written as:

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

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.

Notice the autocomplete: