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<i class="fa fa-check"></i> <b>1.</b> 欢迎使用 Swift
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<i class="fa fa-check"></i> <b>1.1.</b> 关于 Swift
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<i class="fa fa-check"></i> <b>1.2.</b> Swift 初见
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<i class="fa fa-check"></i> <b>2.</b> Swift 教程
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<i class="fa fa-check"></i> <b>2.1.</b> 基础部分
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<i class="fa fa-check"></i> <b>2.2.</b> 基本运算符
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<i class="fa fa-check"></i> <b>2.3.</b> 字符串和字符
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</a>
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<i class="fa fa-check"></i> <b>2.4.</b> 集合类型
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</a>
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<li class="chapter " data-level="2.5" data-path="chapter2/05_Control_Flow.html">
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<a href="../chapter2/05_Control_Flow.html">
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<i class="fa fa-check"></i> <b>2.5.</b> 控制流
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</a>
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<li class="chapter " data-level="2.6" data-path="chapter2/06_Functions.html">
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<a href="../chapter2/06_Functions.html">
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<i class="fa fa-check"></i> <b>2.6.</b> 函数
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</a>
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<li class="chapter " data-level="2.7" data-path="chapter2/07_Closures.html">
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<a href="../chapter2/07_Closures.html">
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<i class="fa fa-check"></i> <b>2.7.</b> 闭包
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</a>
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<li class="chapter " data-level="2.8" data-path="chapter2/08_Enumerations.html">
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<a href="../chapter2/08_Enumerations.html">
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<i class="fa fa-check"></i> <b>2.8.</b> 枚举
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</a>
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<li class="chapter " data-level="2.9" data-path="chapter2/09_Classes_and_Structures.html">
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<a href="../chapter2/09_Classes_and_Structures.html">
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<i class="fa fa-check"></i> <b>2.9.</b> 类和结构体
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</a>
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</li>
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<li class="chapter " data-level="2.10" data-path="chapter2/10_Properties.html">
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<a href="../chapter2/10_Properties.html">
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<i class="fa fa-check"></i> <b>2.10.</b> 属性
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</a>
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<li class="chapter " data-level="2.11" data-path="chapter2/11_Methods.html">
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<a href="../chapter2/11_Methods.html">
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<i class="fa fa-check"></i> <b>2.11.</b> 方法
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</a>
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</li>
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<li class="chapter " data-level="2.12" data-path="chapter2/12_Subscripts.html">
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<a href="../chapter2/12_Subscripts.html">
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<i class="fa fa-check"></i> <b>2.12.</b> 附属脚本
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</a>
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</li>
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<li class="chapter " data-level="2.13" data-path="chapter2/13_Inheritance.html">
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<a href="../chapter2/13_Inheritance.html">
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<i class="fa fa-check"></i> <b>2.13.</b> 继承
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</a>
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</li>
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<li class="chapter " data-level="2.14" data-path="chapter2/14_Initialization.html">
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<a href="../chapter2/14_Initialization.html">
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<i class="fa fa-check"></i> <b>2.14.</b> 构造过程
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</a>
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</li>
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<li class="chapter " data-level="2.15" data-path="chapter2/15_Deinitialization.html">
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<a href="../chapter2/15_Deinitialization.html">
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<i class="fa fa-check"></i> <b>2.15.</b> 析构过程
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</a>
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</li>
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<li class="chapter " data-level="2.16" data-path="chapter2/16_Automatic_Reference_Counting.html">
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<a href="../chapter2/16_Automatic_Reference_Counting.html">
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<i class="fa fa-check"></i> <b>2.16.</b> 自动引用计数
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</a>
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</li>
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<li class="chapter " data-level="2.17" data-path="chapter2/17_Optional_Chaining.html">
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<a href="../chapter2/17_Optional_Chaining.html">
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<i class="fa fa-check"></i> <b>2.17.</b> 可选链
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</a>
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</li>
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<li class="chapter " data-level="2.18" data-path="chapter2/18_Type_Casting.html">
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<a href="../chapter2/18_Type_Casting.html">
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<i class="fa fa-check"></i> <b>2.18.</b> 类型检查
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</a>
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</li>
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<li class="chapter " data-level="2.19" data-path="chapter2/19_Nested_Types.html">
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<a href="../chapter2/19_Nested_Types.html">
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<i class="fa fa-check"></i> <b>2.19.</b> 类型嵌套
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</a>
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</li>
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<li class="chapter " data-level="2.20" data-path="chapter2/20_Extensions.html">
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<a href="../chapter2/20_Extensions.html">
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<i class="fa fa-check"></i> <b>2.20.</b> 扩展
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||
</a>
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||
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</li>
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<li class="chapter " data-level="2.21" data-path="chapter2/21_Protocols.html">
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<a href="../chapter2/21_Protocols.html">
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<i class="fa fa-check"></i> <b>2.21.</b> 协议
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||
</a>
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||
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</li>
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<li class="chapter " data-level="2.22" data-path="chapter2/22_Generics.html">
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<a href="../chapter2/22_Generics.html">
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<i class="fa fa-check"></i> <b>2.22.</b> 泛型
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</a>
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||
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</li>
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<li class="chapter " data-level="2.23" data-path="chapter2/23_Advanced_Operators.html">
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<a href="../chapter2/23_Advanced_Operators.html">
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<i class="fa fa-check"></i> <b>2.23.</b> 高级操作符
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</a>
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</li>
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</ul>
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</li>
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<li class="chapter " data-level="3" data-path="chapter3/chapter3.html">
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<a href="../chapter3/chapter3.html">
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<i class="fa fa-check"></i> <b>3.</b> 语言参考
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</a>
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<ul class="articles">
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<li class="chapter " data-level="3.1" data-path="chapter3/01_About_the_Language_Reference.html">
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<a href="../chapter3/01_About_the_Language_Reference.html">
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<i class="fa fa-check"></i> <b>3.1.</b> 关于语言参考
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</a>
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</li>
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<li class="chapter " data-level="3.2" data-path="chapter3/02_Lexical_Structure.html">
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<a href="../chapter3/02_Lexical_Structure.html">
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<i class="fa fa-check"></i> <b>3.2.</b> 词法结构
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</a>
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</li>
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<li class="chapter " data-level="3.3" data-path="chapter3/03_Types.html">
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<a href="../chapter3/03_Types.html">
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<i class="fa fa-check"></i> <b>3.3.</b> 类型
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</a>
|
||
|
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</li>
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<li class="chapter " data-level="3.4" data-path="chapter3/04_Expressions.html">
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<a href="../chapter3/04_Expressions.html">
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<i class="fa fa-check"></i> <b>3.4.</b> 表达式
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</a>
|
||
|
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</li>
|
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|
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<li class="chapter " data-level="3.5" data-path="chapter3/10_Statements.html">
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<a href="../chapter3/10_Statements.html">
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<i class="fa fa-check"></i> <b>3.5.</b> 语句
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||
</a>
|
||
|
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|
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</li>
|
||
|
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<li class="chapter " data-level="3.6" data-path="chapter3/05_Declarations.html">
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<a href="../chapter3/05_Declarations.html">
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<i class="fa fa-check"></i> <b>3.6.</b> 声明
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||
</a>
|
||
|
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</li>
|
||
|
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<li class="chapter " data-level="3.7" data-path="chapter3/06_Attributes.html">
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<a href="../chapter3/06_Attributes.html">
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<i class="fa fa-check"></i> <b>3.7.</b> 特性
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</a>
|
||
|
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|
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</li>
|
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|
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<li class="chapter " data-level="3.8" data-path="chapter3/07_Patterns.html">
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<a href="../chapter3/07_Patterns.html">
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<i class="fa fa-check"></i> <b>3.8.</b> 模式
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</a>
|
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|
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</li>
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|
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<li class="chapter " data-level="3.9" data-path="chapter3/08_Generic_Parameters_and_Arguments.html">
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<a href="../chapter3/08_Generic_Parameters_and_Arguments.html">
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<i class="fa fa-check"></i> <b>3.9.</b> 泛型参数
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</a>
|
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|
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</li>
|
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|
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<li class="chapter " data-level="3.10" data-path="chapter3/09_Summary_of_the_Grammar.html">
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<a href="../chapter3/09_Summary_of_the_Grammar.html">
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<i class="fa fa-check"></i> <b>3.10.</b> 语法总结
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</a>
|
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|
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</li>
|
||
|
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|
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</ul>
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<a href="../chapter1/02_a_swift_tour.html" title="Swift 初见" class="chapter done " data-progress="1.2" style="left: 7.894736842105263%;"></a>
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<a href="../chapter2/chapter2.html" title="Swift 教程" class="chapter done new-chapter" data-progress="2" style="left: 10.526315789473685%;"></a>
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<a href="../chapter2/01_The_Basics.html" title="基础部分" class="chapter done " data-progress="2.1" style="left: 13.157894736842104%;"></a>
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<a href="../chapter2/10_Properties.html" title="属性" class="chapter done " data-progress="2.10" style="left: 15.789473684210526%;"></a>
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<a href="../chapter2/11_Methods.html" title="方法" class="chapter done " data-progress="2.11" style="left: 18.42105263157895%;"></a>
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<a href="../chapter2/12_Subscripts.html" title="附属脚本" class="chapter done " data-progress="2.12" style="left: 21.05263157894737%;"></a>
|
||
|
||
<a href="../chapter2/13_Inheritance.html" title="继承" class="chapter " data-progress="2.13" style="left: 23.68421052631579%;"></a>
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|
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<a href="../chapter2/14_Initialization.html" title="构造过程" class="chapter " data-progress="2.14" style="left: 26.31578947368421%;"></a>
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<a href="../chapter2/15_Deinitialization.html" title="析构过程" class="chapter " data-progress="2.15" style="left: 28.94736842105263%;"></a>
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<a href="../chapter2/16_Automatic_Reference_Counting.html" title="自动引用计数" class="chapter " data-progress="2.16" style="left: 31.57894736842105%;"></a>
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<a href="../chapter2/17_Optional_Chaining.html" title="可选链" class="chapter " data-progress="2.17" style="left: 34.21052631578947%;"></a>
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<a href="../chapter2/18_Type_Casting.html" title="类型检查" class="chapter " data-progress="2.18" style="left: 36.8421052631579%;"></a>
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<a href="../chapter2/19_Nested_Types.html" title="类型嵌套" class="chapter " data-progress="2.19" style="left: 39.473684210526315%;"></a>
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<a href="../chapter2/02_Basic_Operators.html" title="基本运算符" class="chapter " data-progress="2.2" style="left: 42.10526315789474%;"></a>
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<a href="../chapter2/20_Extensions.html" title="扩展" class="chapter " data-progress="2.20" style="left: 44.73684210526316%;"></a>
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<a href="../chapter2/21_Protocols.html" title="协议" class="chapter " data-progress="2.21" style="left: 47.36842105263158%;"></a>
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<a href="../chapter2/22_Generics.html" title="泛型" class="chapter " data-progress="2.22" style="left: 50%;"></a>
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<a href="../chapter2/23_Advanced_Operators.html" title="高级操作符" class="chapter " data-progress="2.23" style="left: 52.63157894736842%;"></a>
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<a href="../chapter2/03_Strings_and_Characters.html" title="字符串和字符" class="chapter " data-progress="2.3" style="left: 55.26315789473684%;"></a>
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<a href="../chapter2/04_Collection_Types.html" title="集合类型" class="chapter " data-progress="2.4" style="left: 57.89473684210526%;"></a>
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||
|
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<a href="../chapter2/05_Control_Flow.html" title="控制流" class="chapter " data-progress="2.5" style="left: 60.526315789473685%;"></a>
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|
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<a href="../chapter2/06_Functions.html" title="函数" class="chapter " data-progress="2.6" style="left: 63.1578947368421%;"></a>
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<a href="../chapter2/07_Closures.html" title="闭包" class="chapter " data-progress="2.7" style="left: 65.78947368421052%;"></a>
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<a href="../chapter2/08_Enumerations.html" title="枚举" class="chapter " data-progress="2.8" style="left: 68.42105263157895%;"></a>
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<a href="../chapter2/09_Classes_and_Structures.html" title="类和结构体" class="chapter " data-progress="2.9" style="left: 71.05263157894737%;"></a>
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<a href="../chapter3/chapter3.html" title="语言参考" class="chapter new-chapter" data-progress="3" style="left: 73.6842105263158%;"></a>
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<a href="../chapter3/01_About_the_Language_Reference.html" title="关于语言参考" class="chapter " data-progress="3.1" style="left: 76.3157894736842%;"></a>
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||
|
||
<a href="../chapter3/09_Summary_of_the_Grammar.html" title="语法总结" class="chapter " data-progress="3.10" style="left: 78.94736842105263%;"></a>
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||
|
||
<a href="../chapter3/02_Lexical_Structure.html" title="词法结构" class="chapter " data-progress="3.2" style="left: 81.57894736842105%;"></a>
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||
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<a href="../chapter3/03_Types.html" title="类型" class="chapter " data-progress="3.3" style="left: 84.21052631578948%;"></a>
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<a href="../chapter3/04_Expressions.html" title="表达式" class="chapter " data-progress="3.4" style="left: 86.84210526315789%;"></a>
|
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<a href="../chapter3/10_Statements.html" title="语句" class="chapter " data-progress="3.5" style="left: 89.47368421052632%;"></a>
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<a href="../chapter3/05_Declarations.html" title="声明" class="chapter " data-progress="3.6" style="left: 92.10526315789474%;"></a>
|
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|
||
<a href="../chapter3/06_Attributes.html" title="特性" class="chapter " data-progress="3.7" style="left: 94.73684210526316%;"></a>
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||
|
||
<a href="../chapter3/07_Patterns.html" title="模式" class="chapter " data-progress="3.8" style="left: 97.36842105263158%;"></a>
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||
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||
<a href="../chapter3/08_Generic_Parameters_and_Arguments.html" title="泛型参数" class="chapter " data-progress="3.9" style="left: 100%;"></a>
|
||
|
||
</div>
|
||
</div>
|
||
|
||
<div class="page-inner">
|
||
|
||
<section class="normal" id="section-gitbook_142">
|
||
|
||
<blockquote>
|
||
<p>翻译：siemenliu</p>
|
||
<p>校对：zq54zquan</p>
|
||
</blockquote>
|
||
<h1 id="-subscripts-">附属脚本（Subscripts）</h1>
|
||
<hr>
|
||
<p>本页包含内容：</p>
|
||
<ul>
|
||
<li><a href="#subscript_syntax">附属脚本语法</a></li>
|
||
<li><a href="#subscript_usage">附属脚本用法</a></li>
|
||
<li><a href="#subscript_options">附属脚本选项</a></li>
|
||
</ul>
|
||
<p><em>附属脚本</em> 可以定义在类（Class）、结构体（structure）和枚举（enumeration）这些目标中，可以认为是访问对象、集合或序列的快捷方式，不需要再调用实例的特定的赋值和访问方法。举例来说，用附属脚本访问一个数组(Array)实例中的元素可以这样写 <code>someArray[index]</code> ，访问字典(Dictionary)实例中的元素可以这样写 <code>someDictionary[key]</code>。</p>
|
||
<p>对于同一个目标可以定义多个附属脚本，通过索引值类型的不同来进行重载，而且索引值的个数可以是多个。</p>
|
||
<blockquote>
|
||
<p>译者：这里附属脚本重载在本小节中原文并没有任何演示</p>
|
||
</blockquote>
|
||
<p><a name="subscript_syntax"></a></p>
|
||
<h2 id="-">附属脚本语法</h2>
|
||
<p>附属脚本允许你通过在实例后面的方括号中传入一个或者多个的索引值来对实例进行访问和赋值。语法类似于实例方法和计算型属性的混合。与定义实例方法类似，定义附属脚本使用<code>subscript</code>关键字，显式声明入参（一个或多个）和返回类型。与实例方法不同的是附属脚本可以设定为读写或只读。这种方式又有点像计算型属性的getter和setter：</p>
|
||
<pre><code>subscript(index: Int) -> Int {
|
||
get {
|
||
// 返回与入参匹配的Int类型的值
|
||
}
|
||
|
||
set(newValue) {
|
||
// 执行赋值操作
|
||
}
|
||
}
|
||
</code></pre><p><code>newValue</code>的类型必须和附属脚本定义的返回类型相同。与计算型属性相同的是set的入参声明<code>newValue</code>就算不写，在set代码块中依然可以使用默认的<code>newValue</code>这个变量来访问新赋的值。</p>
|
||
<p>与只读计算型属性一样，可以直接将原本应该写在<code>get</code>代码块中的代码写在<code>subscript</code>中：</p>
|
||
<pre><code>subscript(index: Int) -> Int {
|
||
// 返回与入参匹配的Int类型的值
|
||
}
|
||
</code></pre><p>下面代码演示了一个在<code>TimesTable</code>结构体中使用只读附属脚本的用法，该结构体用来展示传入整数的<em>n</em>倍。</p>
|
||
<pre><code>struct TimesTable {
|
||
let multiplier: Int
|
||
subscript(index: Int) -> Int {
|
||
return multiplier * index
|
||
}
|
||
}
|
||
let threeTimesTable = TimesTable(multiplier: 3)
|
||
println("3的6倍是\(threeTimesTable[6])")
|
||
// 输出 "3的6倍是18"
|
||
</code></pre><p>在上例中，通过<code>TimesTable</code>结构体创建了一个用来表示索引值三倍的实例。数值<code>3</code>作为结构体<code>构造函数</code>入参初始化实例成员<code>multiplier</code>。</p>
|
||
<p>你可以通过附属脚本来得到结果，比如<code>threeTimesTable[6]</code>。这条语句访问了<code>threeTimesTable</code>的第六个元素，返回<code>6</code>的<code>3</code>倍即<code>18</code>。</p>
|
||
<blockquote>
|
||
<p>注意：</p>
|
||
<p><code>TimesTable</code>例子是基于一个固定的数学公式。它并不适合开放写权限来对<code>threeTimesTable[someIndex]</code>进行赋值操作，这也是为什么附属脚本只定义为只读的原因。</p>
|
||
</blockquote>
|
||
<p><a name="subscript_usage"></a></p>
|
||
<h2 id="-">附属脚本用法</h2>
|
||
<p>根据使用场景不同附属脚本也具有不同的含义。通常附属脚本是用来访问集合（collection），列表（list）或序列（sequence）中元素的快捷方式。你可以在你自己特定的类或结构体中自由的实现附属脚本来提供合适的功能。</p>
|
||
<p>例如，Swift 的字典（Dictionary）实现了通过附属脚本来对其实例中存放的值进行存取操作。在附属脚本中使用和字典索引相同类型的值，并且把一个字典值类型的值赋值给这个附属脚本来为字典设值：</p>
|
||
<pre><code>var numberOfLegs = ["spider": 8, "ant": 6, "cat": 4]
|
||
numberOfLegs["bird"] = 2
|
||
</code></pre><p>上例定义一个名为<code>numberOfLegs</code>的变量并用一个字典字面量初始化出了包含三对键值的字典实例。<code>numberOfLegs</code>的字典存放值类型推断为<code>Dictionary<String, Int></code>。字典实例创建完成之后通过附属脚本的方式将整型值<code>2</code>赋值到字典实例的索引为<code>bird</code>的位置中。</p>
|
||
<p>更多关于字典（Dictionary）附属脚本的信息请参考<a href="../chapter2/04_Collection_Types.html">读取和修改字典</a></p>
|
||
<blockquote>
|
||
<p>注意：</p>
|
||
<p>Swift 中字典的附属脚本实现中，在<code>get</code>部分返回值是<code>Int?</code>，上例中的<code>numberOfLegs</code>字典通过附属脚本返回的是一个<code>Int?</code>或者说“可选的int”，不是每个字典的索引都能得到一个整型值，对于没有设过值的索引的访问返回的结果就是<code>nil</code>；同样想要从字典实例中删除某个索引下的值也只需要给这个索引赋值为<code>nil</code>即可。</p>
|
||
</blockquote>
|
||
<p><a name="subscript_options"></a></p>
|
||
<h2 id="-">附属脚本选项</h2>
|
||
<p>附属脚本允许任意数量的入参索引，并且每个入参类型也没有限制。附属脚本的返回值也可以是任何类型。附属脚本可以使用变量参数和可变参数，但使用写入读出（in-out）参数或给参数设置默认值都是不允许的。</p>
|
||
<p>一个类或结构体可以根据自身需要提供多个附属脚本实现，在定义附属脚本时通过入参个类型进行区分，使用附属脚本时会自动匹配合适的附属脚本实现运行，这就是<em>附属脚本的重载</em>。</p>
|
||
<p>一个附属脚本入参是最常见的情况，但只要有合适的场景也可以定义多个附属脚本入参。如下例定义了一个<code>Matrix</code>结构体，将呈现一个<code>Double</code>类型的二维矩阵。<code>Matrix</code>结构体的附属脚本需要两个整型参数：</p>
|
||
<pre><code>struct Matrix {
|
||
let rows: Int, columns: Int
|
||
var grid: Double[]
|
||
init(rows: Int, columns: Int) {
|
||
self.rows = rows
|
||
self.columns = columns
|
||
grid = Array(count: rows * columns, repeatedValue: 0.0)
|
||
}
|
||
func indexIsValidForRow(row: Int, column: Int) -> Bool {
|
||
return row >= 0 && row < rows && column >= 0 && column < columns
|
||
}
|
||
subscript(row: Int, column: Int) -> Double {
|
||
get {
|
||
assert(indexIsValidForRow(row, column: column), "Index out of range")
|
||
return grid[(row * columns) + column]
|
||
}
|
||
set {
|
||
assert(indexIsValidForRow(row, column: column), "Index out of range")
|
||
grid[(row * columns) + columns] = newValue
|
||
}
|
||
}
|
||
}
|
||
</code></pre><p><code>Matrix</code>提供了一个两个入参的构造方法，入参分别是<code>rows</code>和<code>columns</code>，创建了一个足够容纳<code>rows * columns</code>个数的<code>Double</code>类型数组。为了存储，将数组的大小和数组每个元素初始值0.0，都传入数组的构造方法中来创建一个正确大小的新数组。关于数组的构造方法和析构方法请参考<a href="../chapter2/04_Collection_Types.html">创建并且构造一个数组</a>。</p>
|
||
<p>你可以通过传入合适的<code>row</code>和<code>column</code>的数量来构造一个新的<code>Matrix</code>实例：</p>
|
||
<pre><code>var matrix = Matrix(rows: 2, columns: 2)
|
||
</code></pre><p>上例中创建了一个新的两行两列的<code>Matrix</code>实例。在阅读顺序从左上到右下的<code>Matrix</code>实例中的数组实例<code>grid</code>是矩阵二维数组的扁平化存储：</p>
|
||
<pre><code>// 示意图
|
||
grid = [0.0, 0.0, 0.0, 0.0]
|
||
|
||
col0 col1
|
||
row0 [0.0, 0.0,
|
||
row1 0.0, 0.0]
|
||
</code></pre><p>将值赋给带有<code>row</code>和<code>column</code>附属脚本的<code>matrix</code>实例表达式可以完成赋值操作，附属脚本入参使用逗号分割</p>
|
||
<pre><code>matrix[0, 1] = 1.5
|
||
matrix[1, 0] = 3.2
|
||
</code></pre><p>上面两条语句分别<code>让matrix</code>的右上值为 1.5，坐下值为 3.2：</p>
|
||
<pre><code>[0.0, 1.5,
|
||
3.2, 0.0]
|
||
</code></pre><p><code>Matrix</code>附属脚本的<code>getter</code>和<code>setter</code>中同时调用了附属脚本入参的<code>row</code>和<code>column</code>是否有效的判断。为了方便进行断言，<code>Matrix</code>包含了一个名为<code>indexIsValid</code>的成员方法，用来确认入参的<code>row</code>或<code>column</code>值是否会造成数组越界：</p>
|
||
<pre><code>func indexIsValidForRow(row: Int, column: Int) -> Bool {
|
||
return row >= 0 && row < rows && column >= 0 && column < columns
|
||
}
|
||
</code></pre><p>断言在附属脚本越界时触发：</p>
|
||
<pre><code>let someValue = matrix[2, 2]
|
||
// 断言将会触发，因为 [2, 2] 已经超过了matrix的最大长度
|
||
</code></pre>
|
||
|
||
</section>
|
||
|
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