函数的定义与调用
func sayHello(personName: String) -> String {
let greeting = "Hello," + personName + "!"
return greeting
}
print(sayHello("Anna"))
// prints "Hello,Anna!"
print(sayHello("Brian"))
// prints "Hello,Brian!"
可变参数
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)
// returns 3.0,which is the arithmetic mean of these five numbers
arithmeticMean(3,8,19)
// returns 10.0,which is the arithmetic mean of these three numbers
一个可变参数（variadic parameter）可以接受一个或多个值。
例如，一个叫做 numbers 的 Double... 型可变参数，在函数体内可以当做一个叫 numbers 的 Double[] 型的数组常量。
常量参数和变量参数
你可以通过指定一个或多个参数为变量参数，从而避免自己在函数中定义新的变量。
输入输出参数
func swapTwoInts(inout a: Int,inout b: Int) {
let temporaryA = a
a = b
b = temporaryA
}
var someInt = 3
var anotherInt = 107
swapTwoInts(&someInt,b: &anotherInt)
print("someInt is now \(someInt),and anotherInt is now \(anotherInt)")
// prints "someInt is now 107,and anotherInt is now 3”
嵌套函数
func chooseStepFunction(backwards: Bool) -> (Int) -> Int {
func stepForward(input: Int) -> Int { return input + 1 }
func stepBackward(input: Int) -> Int { return input - 1 }
return backwards ? stepBackward : stepForward
}
var currentValue = -4
let moveNearerToZero = chooseStepFunction(currentValue > 0)
// moveNearerToZero now refers to the nested stepForward() function
while currentValue != 0 {
print("\(currentValue)... ")
currentValue = moveNearerToZero(currentValue)
}
print("zero!")
// -4...
// -3...
// -2...
// -1...
// zero!
