Swift 闭包表达式-来自CocoaChina

//: Playground - noun: a place where people can play

import UIKit

var title =
"Swift 闭包表达式-来自CocoaChina"

var describe =
"1，利用上下文推断参数和返回值类型;2，单表达式闭包可以省略return关键字;3，参数名称简写;4，Trailing闭包语法"

//1,字母逆序排序

let names = ["China","Alex","Barrt","Ewa","Cocoa","Eye"]

//系统提供sort函数:排序两个参数：a，已经类型的数组；b，排序闭包
(String,String) -> Bool

func backWards(s1:String,s2:String) ->
Bool

{

    return s1 > s2

}

var first =
"第一种排序方式:排序函数"

var firstReversed = names.sorted(by:backWards)

/*

    闭包表达式的形式

    {(parameters) -> returnType in

        statements

    }

 */

var second =
"第二种排序方式:排序内联闭包"

var secondReversed = names.sorted { (s1:String,
s2:String) -> Bool
in

    return s1 > s2

}

// in 表示闭包的参数和返回值类型定义已经完成，闭包函数体即将开始

//根据上下文推断类型

var secondReversedA = names.sorted()

var secondReversedB = names.sorted { (s1, s2) ->
Bool in

    return s1 > s2

}

var third =
"第三种排序方式:运算符函数"

var thirdReversed = names.sorted(by: >)

var trailing = "Trailing闭包"

var trailingDescribe =
"如果是一个很长的闭包表达式作为最后一个参数传递给函数，可以使用trailing闭包增强函数的可读性"

var map = "map方法的使用"

//将Int类型的数组转化为对应的字符串类型的数组

let digitnames = [0:"零",1:"一",2:"二",3:"三",4:"四",5:"五",6:"六",7:"七",8:"八",9:"九"]

let numbers = [14,305,9,94]

let strings = numbers.map { ( num) ->
String in

    

    var str =
""

    var currentNum = num

    

    while currentNum >
0 {

        str =  digitnames[(currentNum%10)]! 
+ str

        currentNum = currentNum/10

    }

    

    return str

}

// ! 代表 force-unwrap

var caputure = "捕获Caputure"

var caputureDescribe =
"闭包可以在其定义的上下文中捕获常量或变量。即使定义这些常量和变量的作用域已经不存在了，闭包仍然可以在闭包函数体内引用和修改这些值"