函数

函数类型作为函数参数

func sum(v1: Int, v2: Int) -> Int {
     return v1 + v2
 }
 
 func difference(v1: Int, v2: Int) -> Int {
      return v1 - v2
 }
 
 func printResult(_ mathFn:(Int,Int) -> Int, _ a: Int, _ b: Int) {
     print("Result: \(mathFn(a,b))")
 }
 
 printResult(sum, 5, 2) // Result: 7
 printResult(difference, 5, 2) // Result: 3

函数类型作为函数返回值

func next(_ input: Int) -> Int {
    return input + 1
 }
 
 func previous(_ input: Int) -> Int {
     return input - 1
 }
 
 func forward(_ forward: Bool) -> (Int) -> Int {
     return forward ? next : previous
 }
 
 forward(true)(3)  // 4
 forward(false)(3) // 2

• 返回值是函数类型的函数，叫做高阶函数（Higher-Order Function）
• typealias用来给类型起别名，如typealias Byte = Int8

typealias Date = (year: Int, momth: Int, day: Int)
 
 func test(_ date: Date) {
     print(date.0)  //2011
     print(date.year) //2011
 }
 test((2011,9,10))