The Swift Programming Language, Apple Inc.,

https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Functions.html#//apple_ref/doc/uid/TP40014097-CH10-ID166

Functions are a

first-class type

Functions can optionally have external parameter names

Functions

func join(s1: String, s2: String, joiner: String) -> String {

  return s1 + joiner + s2

}

join("hello", "world", ", ") //hello, world

//Default Value

func join(s1: String, s2: String, joiner: String = ", ") -> String {

  return s1 + joiner + s2

}

join("hello", "world") //hello, world

//Overload with named parameters

func join(string s1: String, toString s2: String, withJoiner joiner: String = ", ") -> String {

  return s1 + joiner + s2

}

join(string: "hello", toString: "world", withJoiner: ", ")

//Fails due to ambiguous overload

//var joinerFunc: (String, String, String) -> String = join