//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":"yu","pwd":"123","job":"coder"]
user["job"]="student"
print(user)
//user.updateValue("456",forKey:"pwd")//更新值
var old Pwd=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 ：无序的、唯一性、交集并集等集合专有的操作速度
字典：key-value对
*/
