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import UIKit
// 省略外部参数名用"_"
func someFunction(firstParameterName: Int, _ secondParameterName: Int) {
print("\(firstParameterName),\(secondParameterName)")
}
// 函数参数增加缺省值
func aFunction(paremeterWithDefault: Int = 12) {
print("\(paremeterWithDefault)")
}
// 参数数量可变
func arithmeticMean(numbers: Double...) -> Double {
var total: Double = 0
for number in numbers {
total += number
}
return total / Double(numbers.count)
}
// 形参作为变量
func aliginRight(var string: String, totalLength: Int, pad: Character) -> String {
let amountToPad = totalLength - string.characters.count
if amountToPad < 1 {
return string
}
let padString = String(pad)
for _ in 1 ... amountToPad {
string = padString + string
}
return string
}
// 函数操作实参
func swapTwoInts(inout a: Int, inout b: Int) {
let temporyA = a
a = b
b = temporyA
}
// 函数类型
func addTwoInts(a: Int, _ b: Int) -> Int {
return a + b
}
func multiplyTwoInts(a: Int, b: Int) -> Int {
return a * b
}
// 函数作为参数
func printMathResult(mathFunction: (Int, Int) -> Int, _ a: Int, _ b: Int) {
print("Result: \(mathFunction(a, b))")
}
func stepForward(input: Int) -> Int {
return input + 1
}
func stepBackward(input: Int) -> Int {
return input - 1
}
// 函数作为返回值
func chooseStepFunction(backwards: Bool) -> (Int) -> Int {
return backwards ? stepBackward : stepForward
}
// 嵌套函数
func anotherChooseStepFunction(backwards: Bool) -> (Int) -> Int {
func stepForward(input: Int) -> Int {
return input + 1
}
func stepBackward(input: Int) -> Int {
return input - 1
}
return backwards ? stepBackward : stepForward
}
// 闭包
// 闭包形式
// {(<#parameters#>) -> <#returen type#> in
//
// <#statements#>
// }
func backwards(s1: String, s2: String) -> Bool {
return s1 > s2
}
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
/* ------------------------------------------
* 省略外部参数名
* ------------------------------------------*/
someFunction(1, 2)
// 打印 "1,2"
/* ------------------------------------------
* 函数参数增加缺省值
* ------------------------------------------*/
aFunction()
// 打印 "12"
aFunction(22)
// 打印 "22"
/* ------------------------------------------
* 参数数量可变
* ------------------------------------------*/
print("\(arithmeticMean(1, 2, 3, 4, 5))")
// 打印 "3.0"
/* ------------------------------------------
* 形参作为变量
* ------------------------------------------*/
let aliginString = aliginRight("hello", totalLength: 10, pad: "*")
print(aliginString)
// 打印 "*****hello"
/* ------------------------------------------
* 函数操作实参
* ------------------------------------------*/
var someInt = 3
var anotherInt = 10
swapTwoInts(&someInt, b: &anotherInt)
print(" now someInt is \(someInt),anotherInt is \(anotherInt) ")
// 打印 " now someInt is 10,anotherInt is 3"
/* ------------------------------------------
* 函数作为数据类型
* ------------------------------------------*/
var mathFunction:(Int, Int) -> Int = addTwoInts
print("Result: \(mathFunction(2, 3))")
// 打印 "Result: 5"
mathFunction = multiplyTwoInts
print("Result: \(mathFunction(2, 3))")
// 打印 "Result: 6"
/* ------------------------------------------
* 函数作为参数
* ------------------------------------------*/
printMathResult(addTwoInts, 3, 5)
// 打印 "Result: 8"
/* ------------------------------------------
* 函数作为返回值
* ------------------------------------------*/
var currentValue = 3
let moveNearerToZero = chooseStepFunction(currentValue > 0)
while currentValue != 0 {
print("\(currentValue)...")
currentValue = moveNearerToZero(currentValue)
}
print("Zero!")
/* ------------------------------------------
* 闭包
* ------------------------------------------*/
let names = ["Chris", "Alex", "Ewa", "Barry", "Daniella"]
var reversed = names.sort(backwards)
print(reversed)
// 打印 "["Ewa", "Daniella", "Chris", "Barry", "Alex"]"
// 闭包实现
reversed = names.sort({
(s1: String, s2: String) -> Bool in return s1 > s2
})
// 简化
reversed = names.sort({
s1, s2 in return s1 > s2
})
// 单行表达式可以进一步简化
reversed = names.sort({
s1, s2 in s1 > s2
})
// 再次简化
reversed = names.sort({
$0 > $1
})
// 最简
reversed = names.sort(>)
/* ------------------------------------------
* 尾随闭包(Trailing Closure)
* ------------------------------------------*/
//拥有闭包的函数
func someFunctionThatTakesAClosure(closure: () -> Void) {
// 函数体
}
// 没有使用尾随
someFunctionThatTakesAClosure({
// 实现
})
// 使用尾随
someFunctionThatTakesAClosure() {
// 实现
}
// 尾随举例
reversed = names.sort() {$0 > $1}
// 如果闭包是函数的唯一参数,则函数的括号可省
reversed = names.sort {$0 > $1}
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 stringNumbers = numbers.map {
(var number) -> String in
var output = ""
while number > 0 {
output = digitNames[number % 10]! + output
number /= 10
}
return output
}
print(stringNumbers)
// 函数和闭包是值类型,意味着它可以捕获并引用上下文变量的值
var runningTotal = 0
func makeIncreamenter(forIncrement amout: Int) -> () -> Int {
func increment() -> Int {
runningTotal += amout
return runningTotal
}
return increment
}
let incrementByTen = makeIncreamenter(forIncrement: 10)
print(incrementByTen())
// 打印 "10"
print(incrementByTen())
// 打印 "20"
print(runningTotal)
// 打印 "20"
runningTotal = 100
print(incrementByTen())
// 打印 "110"
var customersInLine = ["Chris", "Alex", "Ewa", "Barry", "Daniella"]
func serveCustomer(customerProvider: () -> String) {
print("Now serving \(customerProvider())!")
}
serveCustomer({ customersInLine.removeAtIndex(0) })
// @autoclosure 改变上面的函数,可以省略{}
func anoterServeCustomers(@autoclosure customerProvider: () -> String) {
print("Now serving \(customerProvider())!")
}
anoterServeCustomers(customersInLine.removeAtIndex(0))
// @autoclosure默认@noescape,即闭包不可让外部使用
// 若让外部使用,则用@autoclosure(escaping)修饰
var customerProviders: [() -> String] = []
func collectCustmoerProviders(@autoclosure(escaping) customerProvider: () -> String) {
customerProviders.append(customerProvider)
print("Collected \(customerProviders.count) closure")
}
collectCustmoerProviders(customersInLine.removeAtIndex(0))
collectCustmoerProviders(customersInLine.removeAtIndex(0))
for customerProvider in customerProviders {
print("Now serving \(customerProvider())!")
}
}
}
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