定义

闭包（Closures）是独立的函数代码块，能在代码中传递及使用。

 

语法

{(parameters) -> return type in　　statements} 注：闭包表达式语法可以使用常量参数、变量参数和 inout 类型作为参数，但皆不可提供默认值。

 

范例

func funA(var value : String,closure: (str : String) -> ()) {    closure(str:value)}func closureA(var str : String){    println("closureA : Hi , " + str)}func closureB(var str : String){    println("closureB : Hi , " + str)}funA("cosmokey",closureA)    //closureA : Hi , cosmokeyfunA("cosmokey",closureB)    //closureB : Hi , cosmokeyfunA("cosmokey",{(var str : String) in println("closureC : Hi , " + str)})    //closureC : Hi , cosmokey

 

语法糖

根据上下文推断类型funA("cosmokey",{str in println("closureD : Hi , " + str)})    //closureD : Hi , cosmokey参数名简写funA("cosmokey",{println("closureE : Hi , " + $0)})    //closureE : Hi , cosmokey运算符函数sort(names, >)  //sort(names, { (s1: String, s2: String) -> Bool in return s1 > s2 } )

 

Trailing 闭包

注：Trailing 闭包是一个书写在函数括号之外(之后)的闭包表达式，函数支持将其作为最后一个参数调用。funA("cosmokey"){    str in println("closureF : Hi , " + str)     //closureF : Hi , cosmokey}

 

系统常见闭包：map、filter和reduce

map    map 可以把一个数组按照一定的规则转换成另一个数组    定义        func map(transform: (T) -> U) -> U[]    范例        var oldArray = ["Ping","Cosmokey"]        var newArray = oldArray.map(){
   "Hi , " + $0}    //["Hi , Ping","Hi , Cosmokey"]

filter    filter 起到的就是筛选的功能，参数是一个用来判断是否筛除的筛选闭包    定义            func filter(includeElement: (T) -> Bool) -> [T]        范例        var oldArray = ["Ping","Cosmokey","MM"]        var newArray = oldArray.filter(){count($0) > 2}  //["Ping", "Cosmokey"]

reduce    reduce 函数解决了把数组中的值整合到某个独立对象的问题。    定义        func reduce(initial: U, combine: (U, T) -> U) -> U    范例        var oldArray = ["C","o","s","m","o","k","e","y"]        var newArray = oldArray.reduce("Hi , "){            var newValue = $0 + $1            println(newValue)            return newValue        }        /*        Hi , C        Hi , Co        Hi , Cos        Hi , Cosm        Hi , Cosmo        Hi , Cosmok        Hi , Cosmoke        Hi , Cosmokey        */        println(newArray)        //Hi , Cosmokey