（1）外部参数名可以在函数调用的时候对于参数有更加直观的认识。即该参数名对外部可见。

import Foundation

func sayHello(username name:String)->String{
  
  let result = "Hello," + name
  return result
  
}

var nickname:String = "Jack"

println(sayHello(username: nickname))

同时可以使某个参数名同时是内部参数名和外部参数名：使用#号。

import Foundation

func sayHello(#name:String)->String{
  
  let result = "Hello," + name
  return result
  
}

var nickname:String = "Jack"

println(sayHello(name: nickname))