fun 关键字

Swift 使用func关键字声明函数： 

func greet (name: String, day: String) -> String {
    return "Hello \(name), today is \(day)."
}
greet ("Bob", "Tuesday") 

　　通过元组（Tuple）返回多个值： 

func getGasPrices () -> (Double, Double, Double) {
    return (3.59, 3.69, 3.79)
}
getGasPrices () 

　　支持带有变长参数的函数： 

func sumOf (numbers: Int...) -> Int {
    var sum = 0 for number in numbers {
        sum += number
    }
    return sum
}
sumOf ()
sumOf (42, 597, 12)

　　函数也可以嵌套函数： 

func returnFifteen () -> Int {
    var y = 10
    func add () {
        y += 5
    }
    add ()
    return y
}
returnFifteen ()

　　作为头等对象，函数既可以作为返回值，也可以作为参数传递： 

func makeIncrementer () -> (Int -> Int) {
    func addOne (number: Int) -> Int {
        return 1 + number
    }
    return addOne
}
var increment = makeIncrementer ()
increment (7)  

func hasAnyMatches (list: Int[], condition: Int -> Bool) -> Bool {
    for item in list {
        if condition (item) {
            return true
        }
    }
    return false
}
func lessThanTen (number: Int) -> Bool {
    return number < 10
}
var numbers = [20, 19, 7, 12]
hasAnyMatches (numbers, lessThanTen)