字典的定义

var dict1 = ["swift":"雨燕","python":"大蟒","java":"爪哇国"] 
//问题：dict1 长度是多少？ 3
var dict2:[String:String] = ["swift":"雨燕","python":"大蟒","java":"爪哇国"] 
var dict3:Dictionary<String,String> = ["swift":"雨燕","python":"大蟒","java":"爪哇国"]

//空字典的定义
var empty1:[Int:String] = [:]
var empty2:Dictionary<String,String> = [:]
var empty3 = [String:String]()

//基本操作:长度，判断是否为空，取值

print(dict1.count)
print(dict1.isEmpty)
print(dict1["java"]!)//返回值是一个可选型，通过!进行解包

//字典的特点:1)无序 2)键不能重复
let d1 = [1:"a",2:"b",3:"d"]
let d2 = [2:"b",1:"a",3:"d"]
print(d1==d2)//true 

//let d3 = [2:"b",1:"a",3:"d",3:"e"] --报错

遍历-遍历Key,value,key-value对

for key in dict1.keys{
    print(key)
}

for value in dict1.values{
    print(value)
}

for (key,value) in dict1{
    print(key,value)
}

增删改查

//如果这个Key当前没有，添加操作；如果当前这个Key存在，修改操作
//改
var user=["name":"wei","pwd":"123","job":"coder"]
user["job"] = "student"
print(user)

//user.updateValue("456",forKey:"pwd")//更新值
var oldPwd = user.updateValue("456",forKey:"pwd")!//返回原来value的值
if oldPwd == user["pwd"]{
    print("修改后的密码与修改前一样，可能会导致安全问题！")
}
print(user)

//添加
user["email"] = "56429@qq.com"
user.updateValue("chuzhou",forKey:"location")
print(user)

//删除
user.removeValue(forKey:"location")
user["email"] = nil //null
print(user)

//总结：
数组：有序的；
set: 无序、唯一性、交集并集等集合专有的操作速度高
字典：key-value对