swift:Closure 闭包

@noescape @autoclosure @autoclosure(escaping)

//closures 闭包
let names = ["Chris","Alex","Eva","Barry","Dannis"]
func backward(s1 : String , _ s2:String) ->Bool{
    return s1 > s2
}

var reversed = names.sort(backward)//从高到底 ["Eva", "Dannis", "Chris", "Barry", "Alex"] e d c b a

reversed = names.sort( { (s1: String, s2: String) -> Bool in return s1 > s2 } )  //in 前面的是申明 后面的是函数体

reversed = names.sort( { s1, s2 in return s1 > s2 } )  //omit 参数类型

reversed = names.sort( { s1, s2 in s1 > s2 } )  //omit return

reversed = names.sort({ $0 > $1 })  //简写 省略参数的定义  省略in

reversed = names.sort(>)//["Eva", "Dannis", "Chris", "Barry", "Alex"]

//trailing closures
func someFunctionThatTakesAcloure(closure :() -> Void){
    //function body
    
}
someFunctionThatTakesAcloure({
    //closure body
})


someFunctionThatTakesAcloure(){
    //training closure's body
    
}

reversed = names.sort(){
    $0 > $1
}

reversed = names.sort {
    $0 > $1
}

//map
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{
    (number) -> String in
    var number = number
    var output = ""
    while number > 0{
        output = digitNames[number % 10]! + output
        number /= 10
    }
    return output
    // its value is ["OneSix", "FiveEight", "FiveOneZero"]
}

16 % 10
16 / 10

func makeIncrementer(forIncrement amount: Int) ->() ->Int{
    var runningTotal = 0
    func incrementer() -> Int{
        runningTotal += amount
        return runningTotal
    }
    return incrementer
}
makeIncrementer(forIncrement: 3)
let incrementByTen = makeIncrementer(forIncrement: 10)
incrementByTen()//10
incrementByTen()//20


//Nonescaping cloures  //@noescape 声明函数包 不可以逃  能被@noescape的是As an example, the sort(_:) method takes a closure as its parameter, which is used to compare elements. The parameter is marked @noescape because it is guaranteed not to be needed after sorting is complete.
func someFunctionWithNonescapingClosure(@noescape closure:() ->Void){
    closure()
}

//这里的参数不可以使用 @noescape 他是函数外面声明的一个变量不可以使用@noescape  也就是说直到外部函数执行完成之后才会回调的
var completionHandlers:[() -> Void] = []
func someFunctionWithEscapingClousure(completionHandler:() ->Void){
    completionHandlers.append(completionHandler)
}

//@noescape 标志闭包  和self的作用类似
class SomeClass {
    var x = 10
    func doSomething() {
        someFunctionWithEscapingClousure{ self.x = 100 }
        someFunctionWithNonescapingClosure {x = 200 }
    }
}

let instance = SomeClass()
instance.doSomething()
print(instance.x)
// Prints "200"

completionHandlers.first?()
print(instance.x)
// Prints "100"




//Autocllsures  : the array element isn’t removed until the closure is actually called

var customersInLine = ["Chris", "Alex", "Ewa", "Barry", "Daniella"]
print(customersInLine.count)
// Prints "5"

let customerProvider = { customersInLine.removeAtIndex(0) }

customersInLine  //["Chris", "Alex", "Ewa", "Barry", "Daniella"]

print(customersInLine.count)
// Prints "5"

print("Now serving \(customerProvider())!")
// Prints "Now serving Chris!"

print(customersInLine.count)
// Prints "4"





//@autoclosure   使用@autoclosure标志
func serveCustomer(@autoclosure customerProvider: () -> String) {
    print("Now serving \(customerProvider())!")
}

customersInLine  //["Alex", "Ewa", "Barry", "Daniella"]

serveCustomer(customersInLine.removeAtIndex(0))

customersInLine //["Ewa", "Barry", "Daniella"]
customersInLine.removeAtIndex(0)  //使用@aotolosure 可以使string类型转为closure
// Prints "Now serving Ewa!"

customersInLine  //["Barry", "Daniella"]



// @autoclosure(escaping)
var customerProviders: [() -> String] = [] //[]
func collectCustomerProviders(@autoclosure(escaping) customerProvider: () -> String) {
//      print("Now serving \(customerProvider())!")  只有调用了customerProvider() 才会执行customersInLine.removeAtIndex(0)
    customerProviders.append(customerProvider)
}
customersInLine  //["Barry", "Daniella"]
collectCustomerProviders(customersInLine.removeAtIndex(0))

collectCustomerProviders(customersInLine.removeAtIndex(0))
customersInLine  //["Barry", "Daniella"]

customerProviders //[() -> String, () -> String]


print("Collected \(customerProviders.count) closures.")

// Prints "Collected 2 closures."
for customerProvider in customerProviders {

    print("Now serving \(customerProvider())!")
    

}
customersInLine //[]
// Prints "Now serving Barry!"
// Prints "Now serving Daniella!"