初始化空字符串 ............................................................................................... 59
字符串可变性................................................................................................... 59
字符串是值类型 ............................................................................................... 60
使用字符(Characters) ...................................................................................... 60
计算字符数量................................................................................................... 61
连接字符串和字符............................................................................................ 61
字符串插值 ...................................................................................................... 62
比较字符串 ...................................................................................................... 63
大写和小写字符串............................................................................................ 65
Unicode ........................................................................................................... 65
2.4. 集合类型.......................................................................................................... 68
数组................................................................................................................. 68
字典................................................................................................................. 74
集合的可变性................................................................................................... 79
2.5. 控制流 ............................................................................................................. 79
For 循环.......................................................................................................... 80
While 循环 ...................................................................................................... 84
条件语句.......................................................................................................... 88
控制转移语句................................................................................................... 97
2.6. 函数................................................................................................................103
定义和调用函数 ..............................................................................................104
函数的形参和返回值 .......................................................................................105
函数形参名 .....................................................................................................108
函数类型.........................................................................................................115
嵌套函数.........................................................................................................119
2.7. 闭包................................................................................................................119
闭包表达式 .....................................................................................................120
Trailing 闭包...................................................................................................124
捕获 (Caputure) .............................................................................................127
闭包是引用类型 ..............................................................................................129
2.8. 枚举................................................................................................................130
枚举语法（Enumeration Syntax） ..................................................................130
匹配枚举值和 Switch 语句...............................................................................132
关联值（Associated Values）.........................................................................133
原始值（Raw Values）...................................................................................135
2.9. 类和结构体 .....................................................................................................137
类和结构体对比 ..............................................................................................138
结构体和枚举是值类型....................................................................................141
类是引用类型..................................................................................................143
类和结构体的选择...........................................................................................145
