针对swift4.0函数做一些笔记。
-
普通函数，不做过多笔记
func minMax(array: [Int]) -> (min: Int, max: Int) {
var currentMin = array[0]
var currentMax = array[0]
for value in array[1..<array.count] {
if value < currentMin {
currentMin = value
} else if value > currentMax {
currentMax = value
}
}
return (currentMin, currentMax)
}
-
可变参数函数 (Variadic Parameters)
func arithmeticMean(numbers: Double...) -> Double {
var total: Double = 0
for number in numbers {
total += number
}
return total / Double(numbers.count)
}
arithmeticMean(numbers: 1.0, 2.0, 3.0, 4.0, 5.0)
// result is 3.0
-
输入输出参数函数（In-Out Parameters）
func swapTwoInts(a: inout Int, b: inout Int) {
let temporaryA = a
a = b
b = temporaryA
}
var a = 10
var b = 20
swapTwoInts(a: &a, b: &b)
a // 20
b // 10
-
函数类型(Function Types)
属性
func addTwoInts(_ a: Int, _ b: Int) -> Int {
return a + b
}
var mathFunction: (Int, Int) -> Int = addTwoInts // addTwoInts(_:_:)
mathFunction(2,3) // 5
函数作为参数(Function Types as Parameter Types)
func mathResult(_ mathFunction: (Int, Int) -> Int, _ a: Int, _ b: Int) {
print("result = \(3 * mathFunction(a, b))")
}
mathResult(mathFunction, 2, 3) // result = 15
函数作为返回值(Function Types as Return Types)
func stepForwrad(_ input: Int) -> Int {
return input + 1
}
func stepBackward(_ input: Int) -> Int {
return input - 1
}
func chooseSetpFunction(backward: Bool) -> (Int) -> Int {
return backward ? stepForwrad : stepBackward
}
let moveNearerToZero = chooseSetpFunction(backward: false)
moveNearerToZero(3) // 2
let moveFasterToZero = chooseSetpFunction(backward: true)
moveFasterToZero(4) // 5
-
嵌套函数（Nested Functions）
func chooseStepFunction(backward: Bool) -> (Int) -> Int {
func stepForward(input: Int) -> Int { return input + 1 }
func stepBackward(input: Int) -> Int { return input - 1 }
return backward ? stepForward : stepBackward
}
var currentValue = 4
let moveNearToZero = chooseStepFunction(backward: false)
while currentValue != 0 {
print("\(currentValue)...")
currentValue = moveNearToZero(currentValue)
}
// 4...
// 3...
// 2...
// 1...
