Swift 系统学习 10 字典 Dictionary 增删改查

//: Playground - noun: a place where people can playimport UIKit/* * 本节内容: * 1.字典的声明和初始化 * 2.字典的遍历 * 3.字典的增删改查 *//* * 数组: 有序, 可以重复 * 字典: 无序, 不可重复(key) * 集合: 无序, 不可重复 */// 隐式声明字典[key: value]// 一旦初始化之后, 确定了key和value类型var counties = ["CN": "People Republic Of China", "UK": "United Kindom", "IN": "India"]// 显示声明var countryOne: [String: String] = ["US": "United States"]// 使用四种方式声明不包含key/value的字典var emptyDicOne: [Int: String] = [:] //1.var emptyDicTwo = [Int: String]() //2.var emptyDicThree: Dictionary<Int, String> = [:] //3.var emptyDicFour = Dictionary<Int, String>() //4.// 2和4通过调用init构造创建// 1和3是显示声明key和value// 遍历for key in counties.keys {    print("所有key: \(key)")}for value in counties.values {    print("所有value: \(value)")}for (key, value) in counties {    print("key: \(key) and value: \(value)")}// 查// countryName是String?var countryName = counties["CN"]// countryName可选型counties.count // 多少组key/valueemptyDicFour.isEmptycounties.keys// 值类型(字典)和引用类型counties == countryOne// 增: 对不存在的key设置value就是添加counties["FR"] = "France"counties// 改: 对存在的key设置value就是改counties["UK"] = "Great Britain"counties.updateValue("Britain", forKey: "UK")// 删counties["IN"] = nilcountiescounties.removeValue(forKey: "UK")counties