Swift学习笔记函数

swift的函数和scala的函数有区别，scala的每一个函数都是有返回值的

控制语句if,else也是一个函数，也是有返回值的

而swift不一样，swift的函数可以没有返回值,是有副作用的。

func sayHello(personName:String) -> String{
    let greeting = "Hello, " + personName + "!"
    return greeting
}
println(sayHello("Anna"))
println(sayHello("Brian"))

func halfOpenRangeLength(start: Int,end:Int) -> Int{
    return end - start
}
println(halfOpenRangeLength(1,10))

func count(string:String)->(vowels: Int,consonants: Int, others:Int){
    var vowels = 0, consonants = 0, others = 0
    for character in string{
        switch String(character).lowercaseString{
            case "a", "e", "i", "o", "u":
            ++vowels
            case "b", "c", "d", "f", "g", "h", "j", "k", "l", "m","n", "p", "q", "r", "s", "t", "v", "w", "x", "y", "z":
            ++consonants
        default:
            ++others
        }
    }
    return (vowels, consonants, others)
}

let total = count("some arbitrary string!")

func join(string s1: String, toString s2: String, withJoiner joiner:String = "") -> String{
    return s1 + joiner + s2
}
join(string: "hello", toString: "world", withJoiner: ", ")

func arithmeticMean(numbers: Double...) -> Double{
    var total: Double = 0
    for number in numbers {
        total += number
    }
    return total / Double(numbers.count)
}
arithmeticMean(1,2,3,4,5)

func swapTwoInts(inout a:Int,inout b:Int){
    let temporaryA = a
    a = b
    b = temporaryA
}
var someInt = 3
var anotherInt = 107
swapTwoInts(&someInt, &anotherInt)

上面代码展示了swift里的函数常用方式，与参数定义，方式。

func addTwoInts(a: Int, b: Int) ->Int{
    return a + b
}
var mathFunction: (Int,Int) -> Int = addTwoInts
mathFunction(2,3)

let anotherMathFunction = addTwoInts

anotherMathFunction(1,2)

func stepForward(input: Int) -> Int{
    return input + 1
}
func stepBackward(input: Int) -> Int {
    return input - 1
}
func chooseStepFunction(backwards: Bool) -> (Int) -> Int{
    return backwards ? stepBackward : stepForward
}

chooseStepFunction(true)(2)
var currentValue = 3
while currentValue != 0 {
    println("\(currentValue)...")
    currentValue = chooseStepFunction(true)(currentValue)
}

函数类型,swift里允许使用函数类型，说白了就是函数指针，或者C#里的委托。

var names = ["Chris","Alex","Ewa","Barry","Daniella"]

func backwards(s1: String, s2: String) -> Bool {
return s1 > s2
}
sort(&names, backwards)


sort(&names, { (s1: String, s2: String) -> Bool in
    return s1 > s2
})

sort(&names, {a,b in return a > b })

sort(&names, {a,b in a > b })

sort(&names, { $0 > $1 })

sort(&names) { $0 > $1 }

sort(&names, >)

let digitNames = [
    0: "Zero", 1: "One", 2: "Two", 3: "Three", 4: "Four",
    5: "Five", 6: "Six", 7: "Seven", 8: "Eight", 9: "Nine"
]
let numbers = [16, 58, 510]
let strings = numbers.map{
    (var number)-> String in
    var output = ""
    while number > 0 {
        output = digitNames[number % 10]! + output
        number /= 10
    }
    return output
}

以上是闭包，swift闭包语法上与scala,C#等差不多，也支持捕获外部变量