861 lines
40 KiB
HTML
861 lines
40 KiB
HTML
<!DOCTYPE HTML>
|
||
<html lang="en-US" manifest="../manifest.appcache">
|
||
|
||
<head prefix="og: http://ogp.me/ns# book: http://ogp.me/ns/book#">
|
||
|
||
|
||
<meta charset="UTF-8">
|
||
<title>扩展 | Swift 编程语言</title>
|
||
|
||
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
|
||
<meta name="robots" content="index, follow">
|
||
<meta name="author" content="">
|
||
<meta name="description" content="Swift 是苹果在 WWDC 2014 上发布的一款全新的编程语言，本书译自苹果官方的 Swift 教程《The Swift Programming Language》。">
|
||
<meta name="keywords" content="gitbook,github" >
|
||
<meta name="generator" content="www.gitbook.io">
|
||
|
||
|
||
<link rel="next" href="../chapter2/21_Protocols.html" />
|
||
|
||
|
||
<link rel="prev" href="../chapter2/19_Nested_Types.html" />
|
||
|
||
|
||
<meta property="og:title" content="扩展 | Swift 编程语言">
|
||
<meta property="og:site_name" content="Swift 编程语言">
|
||
<meta property="og:type" content="book">
|
||
<meta property="og:locale" content="en_US">
|
||
|
||
<meta property="book:author" content="https://github.com/">
|
||
<meta property="book:tag" content="GitBook">
|
||
|
||
<meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no">
|
||
<meta name="apple-mobile-web-app-capable" content="yes">
|
||
<meta name="apple-mobile-web-app-status-bar-style" content="black">
|
||
|
||
<link rel="shortcut icon" href="../gitbook/images/favicon.ico" type="image/x-icon">
|
||
|
||
|
||
</head>
|
||
<body>
|
||
|
||
|
||
|
||
<link rel="stylesheet" href="../gitbook/style.css">
|
||
|
||
|
||
|
||
|
||
<div class="book" data-level="2.20" data-basepath=".." data-revision="1402402017737">
|
||
<div class="book-header">
|
||
<!-- Actions Left -->
|
||
<a href="#" class="btn pull-left toggle-summary" aria-label="Toggle summary"><i class="fa fa-align-justify"></i></a>
|
||
|
||
<a href="https://github.com/null" target="_blank" class="btn pull-left home-bookmark" aria-label="GitHub home"><i class="fa fa-bookmark-o"></i></a>
|
||
|
||
<a href="#" class="btn pull-left toggle-search" aria-label="Toggle search"><i class="fa fa-search"></i></a>
|
||
<span id="font-settings-wrapper">
|
||
<a href="#" class="btn pull-left toggle-font-settings" aria-label="Toggle font settings"><i class="fa fa-font"></i>
|
||
</a>
|
||
<div class="dropdown-menu font-settings">
|
||
<div class="dropdown-caret">
|
||
<span class="caret-outer"></span>
|
||
<span class="caret-inner"></span>
|
||
</div>
|
||
|
||
<div class="btn-group btn-block">
|
||
<button id="reduce-font-size" class="btn btn-default">A</button>
|
||
<button id="enlarge-font-size" class="btn btn-default">A</button>
|
||
</div>
|
||
|
||
<ul class="list-group font-family-list">
|
||
<li class="list-group-item" data-font="0">Serif</li>
|
||
<li class="list-group-item" data-font="1">Sans</li>
|
||
</ul>
|
||
|
||
<div class="btn-group btn-group-xs btn-block color-theme-list">
|
||
<button type="button" class="btn btn-default" id="color-theme-preview-0" data-theme="0">White</button>
|
||
<button type="button" class="btn btn-default" id="color-theme-preview-1" data-theme="1">Sepia</button>
|
||
<button type="button" class="btn btn-default" id="color-theme-preview-2" data-theme="2">Night</button>
|
||
</div>
|
||
</div>
|
||
|
||
</span>
|
||
|
||
<!-- Actions Right -->
|
||
|
||
<a href="#" target="_blank" class="btn pull-right google-plus-sharing-link sharing-link" data-sharing="google-plus" aria-label="Share on Google Plus"><i class="fa fa-google-plus"></i></a>
|
||
|
||
|
||
<a href="#" target="_blank" class="btn pull-right facebook-sharing-link sharing-link" data-sharing="facebook" aria-label="Share on Facebook"><i class="fa fa-facebook"></i></a>
|
||
|
||
|
||
<a href="#" target="_blank" class="btn pull-right twitter-sharing-link sharing-link" data-sharing="twitter" aria-label="Share on Twitter"><i class="fa fa-twitter"></i></a>
|
||
|
||
|
||
|
||
|
||
<!-- Title -->
|
||
<h1>
|
||
<i class="fa fa-spinner fa-spin"></i>
|
||
<a href="../" >Swift 编程语言</a>
|
||
</h1>
|
||
</div>
|
||
|
||
|
||
|
||
<div class="book-summary">
|
||
<div class="book-search">
|
||
<input type="text" placeholder="Search" class="form-control" />
|
||
</div>
|
||
<ul class="summary">
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li data-level="0" data-path="index.html">
|
||
<a href="../"><i class="fa fa-check"></i> Introduction</a>
|
||
</li>
|
||
|
||
|
||
<li class="chapter " data-level="1" data-path="chapter1/chapter1.html">
|
||
|
||
<a href="../chapter1/chapter1.html">
|
||
<i class="fa fa-check"></i> <b>1.</b> 欢迎使用 Swift
|
||
</a>
|
||
|
||
|
||
<ul class="articles">
|
||
|
||
|
||
<li class="chapter " data-level="1.1" data-path="chapter1/01_swift.html">
|
||
|
||
<a href="../chapter1/01_swift.html">
|
||
<i class="fa fa-check"></i> <b>1.1.</b> 关于 Swift
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="1.2" data-path="chapter1/02_a_swift_tour.html">
|
||
|
||
<a href="../chapter1/02_a_swift_tour.html">
|
||
<i class="fa fa-check"></i> <b>1.2.</b> Swift 初见
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
|
||
</ul>
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2" data-path="chapter2/chapter2.html">
|
||
|
||
<a href="../chapter2/chapter2.html">
|
||
<i class="fa fa-check"></i> <b>2.</b> Swift 教程
|
||
</a>
|
||
|
||
|
||
<ul class="articles">
|
||
|
||
|
||
<li class="chapter " data-level="2.1" data-path="chapter2/01_The_Basics.html">
|
||
|
||
<a href="../chapter2/01_The_Basics.html">
|
||
<i class="fa fa-check"></i> <b>2.1.</b> 基础部分
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.2" data-path="chapter2/02_Basic_Operators.html">
|
||
|
||
<a href="../chapter2/02_Basic_Operators.html">
|
||
<i class="fa fa-check"></i> <b>2.2.</b> 基本运算符
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.3" data-path="chapter2/03_Strings_and_Characters.html">
|
||
|
||
<a href="../chapter2/03_Strings_and_Characters.html">
|
||
<i class="fa fa-check"></i> <b>2.3.</b> 字符串和字符
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.4" data-path="chapter2/04_Collection_Types.html">
|
||
|
||
<a href="../chapter2/04_Collection_Types.html">
|
||
<i class="fa fa-check"></i> <b>2.4.</b> 集合类型
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.5" data-path="chapter2/05_Control_Flow.html">
|
||
|
||
<a href="../chapter2/05_Control_Flow.html">
|
||
<i class="fa fa-check"></i> <b>2.5.</b> 控制流
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.6" data-path="chapter2/06_Functions.html">
|
||
|
||
<a href="../chapter2/06_Functions.html">
|
||
<i class="fa fa-check"></i> <b>2.6.</b> 函数
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.7" data-path="chapter2/07_Closures.html">
|
||
|
||
<a href="../chapter2/07_Closures.html">
|
||
<i class="fa fa-check"></i> <b>2.7.</b> 闭包
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.8" data-path="chapter2/08_Enumerations.html">
|
||
|
||
<a href="../chapter2/08_Enumerations.html">
|
||
<i class="fa fa-check"></i> <b>2.8.</b> 枚举
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.9" data-path="chapter2/09_Classes_and_Structures.html">
|
||
|
||
<a href="../chapter2/09_Classes_and_Structures.html">
|
||
<i class="fa fa-check"></i> <b>2.9.</b> 类和结构体
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.10" data-path="chapter2/10_Properties.html">
|
||
|
||
<a href="../chapter2/10_Properties.html">
|
||
<i class="fa fa-check"></i> <b>2.10.</b> 属性
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.11" data-path="chapter2/11_Methods.html">
|
||
|
||
<a href="../chapter2/11_Methods.html">
|
||
<i class="fa fa-check"></i> <b>2.11.</b> 方法
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.12" data-path="chapter2/12_Subscripts.html">
|
||
|
||
<a href="../chapter2/12_Subscripts.html">
|
||
<i class="fa fa-check"></i> <b>2.12.</b> 附属脚本
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.13" data-path="chapter2/13_Inheritance.html">
|
||
|
||
<a href="../chapter2/13_Inheritance.html">
|
||
<i class="fa fa-check"></i> <b>2.13.</b> 继承
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.14" data-path="chapter2/14_Initialization.html">
|
||
|
||
<a href="../chapter2/14_Initialization.html">
|
||
<i class="fa fa-check"></i> <b>2.14.</b> 构造过程
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.15" data-path="chapter2/15_Deinitialization.html">
|
||
|
||
<a href="../chapter2/15_Deinitialization.html">
|
||
<i class="fa fa-check"></i> <b>2.15.</b> 析构过程
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.16" data-path="chapter2/16_Automatic_Reference_Counting.html">
|
||
|
||
<a href="../chapter2/16_Automatic_Reference_Counting.html">
|
||
<i class="fa fa-check"></i> <b>2.16.</b> 自动引用计数
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.17" data-path="chapter2/17_Optional_Chaining.html">
|
||
|
||
<a href="../chapter2/17_Optional_Chaining.html">
|
||
<i class="fa fa-check"></i> <b>2.17.</b> 可选链
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.18" data-path="chapter2/18_Type_Casting.html">
|
||
|
||
<a href="../chapter2/18_Type_Casting.html">
|
||
<i class="fa fa-check"></i> <b>2.18.</b> 类型检查
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.19" data-path="chapter2/19_Nested_Types.html">
|
||
|
||
<a href="../chapter2/19_Nested_Types.html">
|
||
<i class="fa fa-check"></i> <b>2.19.</b> 嵌套类型
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.20" data-path="chapter2/20_Extensions.html">
|
||
|
||
<a href="../chapter2/20_Extensions.html">
|
||
<i class="fa fa-check"></i> <b>2.20.</b> 扩展
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.21" data-path="chapter2/21_Protocols.html">
|
||
|
||
<a href="../chapter2/21_Protocols.html">
|
||
<i class="fa fa-check"></i> <b>2.21.</b> 协议
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.22" data-path="chapter2/22_Generics.html">
|
||
|
||
<a href="../chapter2/22_Generics.html">
|
||
<i class="fa fa-check"></i> <b>2.22.</b> 泛型
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="2.23" data-path="chapter2/23_Advanced_Operators.html">
|
||
|
||
<a href="../chapter2/23_Advanced_Operators.html">
|
||
<i class="fa fa-check"></i> <b>2.23.</b> 高级操作符
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
|
||
</ul>
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="3" data-path="chapter3/chapter3.html">
|
||
|
||
<a href="../chapter3/chapter3.html">
|
||
<i class="fa fa-check"></i> <b>3.</b> 语言参考
|
||
</a>
|
||
|
||
|
||
<ul class="articles">
|
||
|
||
|
||
<li class="chapter " data-level="3.1" data-path="chapter3/01_About_the_Language_Reference.html">
|
||
|
||
<a href="../chapter3/01_About_the_Language_Reference.html">
|
||
<i class="fa fa-check"></i> <b>3.1.</b> 关于语言参考
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="3.2" data-path="chapter3/02_Lexical_Structure.html">
|
||
|
||
<a href="../chapter3/02_Lexical_Structure.html">
|
||
<i class="fa fa-check"></i> <b>3.2.</b> 词法结构
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="3.3" data-path="chapter3/03_Types.html">
|
||
|
||
<a href="../chapter3/03_Types.html">
|
||
<i class="fa fa-check"></i> <b>3.3.</b> 类型
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="3.4" data-path="chapter3/04_Expressions.html">
|
||
|
||
<a href="../chapter3/04_Expressions.html">
|
||
<i class="fa fa-check"></i> <b>3.4.</b> 表达式
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="3.5" data-path="chapter3/10_Statements.html">
|
||
|
||
<a href="../chapter3/10_Statements.html">
|
||
<i class="fa fa-check"></i> <b>3.5.</b> 语句
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="3.6" data-path="chapter3/05_Declarations.html">
|
||
|
||
<a href="../chapter3/05_Declarations.html">
|
||
<i class="fa fa-check"></i> <b>3.6.</b> 声明
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="3.7" data-path="chapter3/06_Attributes.html">
|
||
|
||
<a href="../chapter3/06_Attributes.html">
|
||
<i class="fa fa-check"></i> <b>3.7.</b> 特性
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="3.8" data-path="chapter3/07_Patterns.html">
|
||
|
||
<a href="../chapter3/07_Patterns.html">
|
||
<i class="fa fa-check"></i> <b>3.8.</b> 模式
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="3.9" data-path="chapter3/08_Generic_Parameters_and_Arguments.html">
|
||
|
||
<a href="../chapter3/08_Generic_Parameters_and_Arguments.html">
|
||
<i class="fa fa-check"></i> <b>3.9.</b> 泛型参数
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
<li class="chapter " data-level="3.10" data-path="chapter3/09_Summary_of_the_Grammar.html">
|
||
|
||
<a href="../chapter3/09_Summary_of_the_Grammar.html">
|
||
<i class="fa fa-check"></i> <b>3.10.</b> 语法总结
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
||
|
||
</ul>
|
||
|
||
</li>
|
||
|
||
|
||
|
||
|
||
<li class="divider"></li>
|
||
<li>
|
||
<a href="http://www.gitbook.io/" target="blank" class="gitbook-link">Generated using GitBook</a>
|
||
</li>
|
||
<li style="margin-left:15%;"> <iframe src="http://ghbtns.com/github-btn.html?user=numbbbbb&repo=the-swift-programming-language-in-chinese&type=watch&count=true&size=large"
|
||
allowtransparency="true" frameborder="0" scrolling="0" width="170" height="30"></iframe></li>
|
||
</ul>
|
||
</div>
|
||
|
||
<div class="book-body">
|
||
<div class="body-inner">
|
||
<div class="page-wrapper" tabindex="-1">
|
||
<div class="book-progress">
|
||
<div class="bar">
|
||
<div class="inner" style="width: 44.73684210526316%;min-width: 42.10526315789474%;"></div>
|
||
</div>
|
||
<div class="chapters">
|
||
|
||
<a href="../index.html" title="Introduction" class="chapter done new-chapter" data-progress="0" style="left: 0%;"></a>
|
||
|
||
<a href="../chapter1/chapter1.html" title="欢迎使用 Swift" class="chapter done new-chapter" data-progress="1" style="left: 2.6315789473684212%;"></a>
|
||
|
||
<a href="../chapter1/01_swift.html" title="关于 Swift" class="chapter done " data-progress="1.1" style="left: 5.2631578947368425%;"></a>
|
||
|
||
<a href="../chapter1/02_a_swift_tour.html" title="Swift 初见" class="chapter done " data-progress="1.2" style="left: 7.894736842105263%;"></a>
|
||
|
||
<a href="../chapter2/chapter2.html" title="Swift 教程" class="chapter done new-chapter" data-progress="2" style="left: 10.526315789473685%;"></a>
|
||
|
||
<a href="../chapter2/01_The_Basics.html" title="基础部分" class="chapter done " data-progress="2.1" style="left: 13.157894736842104%;"></a>
|
||
|
||
<a href="../chapter2/10_Properties.html" title="属性" class="chapter done " data-progress="2.10" style="left: 15.789473684210526%;"></a>
|
||
|
||
<a href="../chapter2/11_Methods.html" title="方法" class="chapter done " data-progress="2.11" style="left: 18.42105263157895%;"></a>
|
||
|
||
<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 done " data-progress="2.13" style="left: 23.68421052631579%;"></a>
|
||
|
||
<a href="../chapter2/14_Initialization.html" title="构造过程" class="chapter done " data-progress="2.14" style="left: 26.31578947368421%;"></a>
|
||
|
||
<a href="../chapter2/15_Deinitialization.html" title="析构过程" class="chapter done " data-progress="2.15" style="left: 28.94736842105263%;"></a>
|
||
|
||
<a href="../chapter2/16_Automatic_Reference_Counting.html" title="自动引用计数" class="chapter done " data-progress="2.16" style="left: 31.57894736842105%;"></a>
|
||
|
||
<a href="../chapter2/17_Optional_Chaining.html" title="可选链" class="chapter done " data-progress="2.17" style="left: 34.21052631578947%;"></a>
|
||
|
||
<a href="../chapter2/18_Type_Casting.html" title="类型检查" class="chapter done " data-progress="2.18" style="left: 36.8421052631579%;"></a>
|
||
|
||
<a href="../chapter2/19_Nested_Types.html" title="嵌套类型" class="chapter done " data-progress="2.19" style="left: 39.473684210526315%;"></a>
|
||
|
||
<a href="../chapter2/02_Basic_Operators.html" title="基本运算符" class="chapter done " data-progress="2.2" style="left: 42.10526315789474%;"></a>
|
||
|
||
<a href="../chapter2/20_Extensions.html" title="扩展" class="chapter done " data-progress="2.20" style="left: 44.73684210526316%;"></a>
|
||
|
||
<a href="../chapter2/21_Protocols.html" title="协议" class="chapter " data-progress="2.21" style="left: 47.36842105263158%;"></a>
|
||
|
||
<a href="../chapter2/22_Generics.html" title="泛型" class="chapter " data-progress="2.22" style="left: 50%;"></a>
|
||
|
||
<a href="../chapter2/23_Advanced_Operators.html" title="高级操作符" class="chapter " data-progress="2.23" style="left: 52.63157894736842%;"></a>
|
||
|
||
<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>
|
||
|
||
<a href="../chapter2/04_Collection_Types.html" title="集合类型" class="chapter " data-progress="2.4" style="left: 57.89473684210526%;"></a>
|
||
|
||
<a href="../chapter2/05_Control_Flow.html" title="控制流" class="chapter " data-progress="2.5" style="left: 60.526315789473685%;"></a>
|
||
|
||
<a href="../chapter2/06_Functions.html" title="函数" class="chapter " data-progress="2.6" style="left: 63.1578947368421%;"></a>
|
||
|
||
<a href="../chapter2/07_Closures.html" title="闭包" class="chapter " data-progress="2.7" style="left: 65.78947368421052%;"></a>
|
||
|
||
<a href="../chapter2/08_Enumerations.html" title="枚举" class="chapter " data-progress="2.8" style="left: 68.42105263157895%;"></a>
|
||
|
||
<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>
|
||
|
||
<a href="../chapter3/chapter3.html" title="语言参考" class="chapter new-chapter" data-progress="3" style="left: 73.6842105263158%;"></a>
|
||
|
||
<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>
|
||
|
||
<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>
|
||
|
||
<a href="../chapter3/02_Lexical_Structure.html" title="词法结构" class="chapter " data-progress="3.2" style="left: 81.57894736842105%;"></a>
|
||
|
||
<a href="../chapter3/03_Types.html" title="类型" class="chapter " data-progress="3.3" style="left: 84.21052631578948%;"></a>
|
||
|
||
<a href="../chapter3/04_Expressions.html" title="表达式" class="chapter " data-progress="3.4" style="left: 86.84210526315789%;"></a>
|
||
|
||
<a href="../chapter3/10_Statements.html" title="语句" class="chapter " data-progress="3.5" style="left: 89.47368421052632%;"></a>
|
||
|
||
<a href="../chapter3/05_Declarations.html" title="声明" class="chapter " data-progress="3.6" style="left: 92.10526315789474%;"></a>
|
||
|
||
<a href="../chapter3/06_Attributes.html" title="特性" class="chapter " data-progress="3.7" style="left: 94.73684210526316%;"></a>
|
||
|
||
<a href="../chapter3/07_Patterns.html" title="模式" class="chapter " data-progress="3.8" style="left: 97.36842105263158%;"></a>
|
||
|
||
<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_59">
|
||
|
||
<h1 id="-extensions-">扩展（Extensions）</h1>
|
||
<hr>
|
||
<p>本页包含内容：</p>
|
||
<ul>
|
||
<li>扩展语法（Extension Syntax）</li>
|
||
<li>计算属性（Computed Properties）</li>
|
||
<li>构造器（Initializers）</li>
|
||
<li>方法（Methods）</li>
|
||
<li>下标（Subscripts）</li>
|
||
<li>嵌套类型（Nested Types）</li>
|
||
</ul>
|
||
<p><em>扩展</em>就是向一个已有的类、结构体或枚举类型添加新功能（functionality）。这包括在没有权限获取原始源代码的情况下扩展类型的能力（即<em>逆向建模</em>）。扩展和Objective-C中的分类(categories)类似。（不过与Objective-C不同的是，Swift的扩展没有名字。）</p>
|
||
<p>Swift中的扩展可以：</p>
|
||
<ul>
|
||
<li>添加计算属性和计算静态属性</li>
|
||
<li>定义实例方法和类型方法</li>
|
||
<li>提供新的构造器</li>
|
||
<li>定义下标</li>
|
||
<li>定义和使用新的嵌套类型</li>
|
||
<li>使一个已有类型符合某个接口</li>
|
||
</ul>
|
||
<blockquote>
|
||
<p>注意
|
||
如果你定义了一个扩展向一个已有类型添加新功能，那么这个新功能对该类型的所有已有实例中都是可用的，即使它们是在你的这个扩展的前面定义的。</p>
|
||
</blockquote>
|
||
<h2 id="-">扩展语法</h2>
|
||
<p>声明一个扩展使用关键字<code>extension</code>：</p>
|
||
<pre><code class="lang-javascript">extension SomeType{
|
||
<span class="hljs-comment">// new functionality to add to SomeType goes here</span>
|
||
}
|
||
</code></pre>
|
||
<p>一个扩展可以扩展一个已有类型，使其能够适配一个或多个接口。当这种情况发生时，接口的名字应该完全按照类或结构体的名字的方式进行书写：</p>
|
||
<pre><code class="lang-javascript">extension SomeType: SomeProtocol, AnotherProctocol{
|
||
<span class="hljs-comment">// implementation of protocol requirments goes here</span>
|
||
}
|
||
</code></pre>
|
||
<p>按照这种方式添加的接口一致性被称之为<strong>给扩展添加接口一致性(Protocal Conformance)</strong></p>
|
||
<h2 id="-">计算属性</h2>
|
||
<p>扩展可以向已有类型添加计算实例属性和计算类型属性。下面的例子向Swift的内建<code>Double</code>类型添加了5个计算实例属性，从而提供与距离单位协作的基本支持。</p>
|
||
<pre><code class="lang-javascript">extension Double{
|
||
<span class="hljs-keyword">var</span> km: Double { <span class="hljs-keyword">return</span> self * <span class="hljs-number">1</span>_000<span class="hljs-number">.0</span> }
|
||
<span class="hljs-keyword">var</span> m : Double { <span class="hljs-keyword">return</span> self }
|
||
<span class="hljs-keyword">var</span> cm: Double { <span class="hljs-keyword">return</span> self / <span class="hljs-number">100.0</span> }
|
||
<span class="hljs-keyword">var</span> mm: Double { <span class="hljs-keyword">return</span> self / <span class="hljs-number">1</span>_000<span class="hljs-number">.0</span> }
|
||
<span class="hljs-keyword">var</span> ft: Double { <span class="hljs-keyword">return</span> self / <span class="hljs-number">3.28084</span> }
|
||
}
|
||
<span class="hljs-keyword">let</span> oneInch = <span class="hljs-number">25.4</span>.mm
|
||
println(<span class="hljs-string">"One inch is \(oneInch) meters"</span>)
|
||
<span class="hljs-comment">// prints "One inch is 0.0254 meters"</span>
|
||
<span class="hljs-keyword">let</span> threeFeet = <span class="hljs-number">3.</span>ft
|
||
println(<span class="hljs-string">"Three feet is \(threeFeet) meters"</span>)
|
||
<span class="hljs-comment">// prints "Three feet is 0.914399970739201 meters"</span>
|
||
</code></pre>
|
||
<p>这些计算属性表达的含义是把一个<code>Double</code>型的值看作是某单位下的长度值。即使它们被实现为计算属性，但这些属性仍可以接一个带有dot语法的浮点型字面值，而这恰恰是使用这些浮点型字面量实现距离转换的方式。</p>
|
||
<p>在上述例子中，一个<code>Double</code>型的值<code>1.0</code>被用来表示“1米”。这就是为什么<code>m</code>计算属性返回<code>self</code>——表达式<code>1.m</code>被认为是计算<code>1.0</code>的<code>Double</code>值。</p>
|
||
<p>其它单位则需要一些转换来表示在米下测量的值。1千米等于1,000米，所以<code>km</code>计算属性要把值乘以<code>1_000.00</code>来转化成单位米下的数值。类似地，1米有3.28024英尺，所以<code>ft</code>计算属性要把对应的<code>Double</code>值除以<code>3.28024</code>来实现英尺到米的单位换算。</p>
|
||
<p>这些属性是只读的计算属性，所有从简考虑它们不用<code>get</code>关键字表示。它们的返回值是<code>Double</code>型，而且可以用于所有接受<code>Double</code>的数学计算中：</p>
|
||
<pre><code class="lang-javascript"><span class="hljs-keyword">let</span> aMarathon = <span class="hljs-number">42.</span>km + <span class="hljs-number">195.</span>m
|
||
println(<span class="hljs-string">"A marathon is \(aMarathon) meters long"</span>)
|
||
<span class="hljs-comment">// prints "A marathon is 42495.0 meters long"</span>
|
||
</code></pre>
|
||
<blockquote>
|
||
<p>注意
|
||
扩展可以添加新的计算属性，但是不可以添加存储属性，也不可以向已有属性添加属性观测器(property observers)。</p>
|
||
</blockquote>
|
||
<h2 id="-">构造器</h2>
|
||
<p>扩展可以向已有类型添加新的构造器。这可以让你扩展其它类型，将你自己的定制类型作为构造器参数，或者提供该类型的原始实现中没有包含的额外初始化选项。</p>
|
||
<blockquote>
|
||
<p>注意
|
||
如果你使用扩展向一个值类型添加一个构造器，该构造器向所有的存储属性提供默认值，而且没有定义任何定制构造器（custom initializers），那么对于来自你的扩展构造器中的值类型，你可以调用默认构造器(default initializers)和成员级构造器(memberwise initializers)。
|
||
正如在值类型的构造器授权中描述的，如果你已经把构造器写成值类型原始实现的一部分，上述规则不再适用。</p>
|
||
</blockquote>
|
||
<p>下面的例子定义了一个用于描述几何矩形的定制结构体<code>Rect</code>。这个例子同时定义了两个辅助结构体<code>Size</code>和<code>Point</code>，它们都把<code>0.0</code>作为所有属性的默认值：</p>
|
||
<pre><code class="lang-javascript">struct Size{
|
||
<span class="hljs-keyword">var</span> width = <span class="hljs-number">0.0</span>, height = <span class="hljs-number">0.0</span>
|
||
}
|
||
struct Point{
|
||
<span class="hljs-keyword">var</span> x = <span class="hljs-number">0.0</span>, y = <span class="hljs-number">0.0</span>
|
||
}
|
||
struct Rect{
|
||
<span class="hljs-keyword">var</span> origin = Point()
|
||
<span class="hljs-keyword">var</span> size = Size()
|
||
}
|
||
</code></pre>
|
||
<p>因为结构体<code>Rect</code>提供了其所有属性的默认值，所以正如默认构造器中描述的，它可以自动接受一个默认的构造器和一个成员级构造器。这些构造器可以用于构造新的<code>Rect</code>实例：</p>
|
||
<pre><code class="lang-javascript"><span class="hljs-keyword">let</span> defaultRect = Rect()
|
||
<span class="hljs-keyword">let</span> memberwiseRect = Rect(origin: Point(x: <span class="hljs-number">2.0</span>, y: <span class="hljs-number">2.0</span>),
|
||
size: Size(width: <span class="hljs-number">5.0</span>, height: <span class="hljs-number">5.0</span>))
|
||
</code></pre>
|
||
<p>你可以提供一个额外的使用特殊中心点和大小的构造器来扩展<code>Rect</code>结构体：</p>
|
||
<pre><code class="lang-javascript">extension Rect{
|
||
init(center: Point, size: Size){
|
||
<span class="hljs-keyword">let</span> originX = center.x - (size.width / <span class="hljs-number">2</span>)
|
||
<span class="hljs-keyword">let</span> originY = center.y - (size.height / <span class="hljs-number">2</span>)
|
||
self.init(origin: Point(x: originX, y: originY), size: size)
|
||
}
|
||
}
|
||
</code></pre>
|
||
<p>这个新的构造器首先根据提供的<code>center</code>和<code>size</code>值计算一个合适的原点。然后调用该结构体自动的成员构造器<code>init(origin:size:)</code>，该构造器将新的原点和大小存到了合适的属性中：</p>
|
||
<pre><code class="lang-javascript"><span class="hljs-keyword">let</span> centerRect = Rect(center: Point(x: <span class="hljs-number">4.0</span>, y: <span class="hljs-number">4.0</span>),
|
||
size: Size(width: <span class="hljs-number">3.0</span>, height: <span class="hljs-number">3.0</span>))
|
||
<span class="hljs-comment">// centerRect's origin is (2.5, 2.5) and its size is (3.0, 3.0)</span>
|
||
</code></pre>
|
||
<blockquote>
|
||
<p>注意
|
||
如果你使用扩展提供了一个新的构造器，你依旧有责任保证构造过程能够让所有实例完全初始化。</p>
|
||
</blockquote>
|
||
<h2 id="-">方法</h2>
|
||
<p>扩展可以向已有类型添加新的实例方法和类型方法。下面的例子向<code>Int</code>类型添加一个名为<code>repetitions</code>的新实例方法：</p>
|
||
<pre><code class="lang-javascript">extension Int{
|
||
func repetitions(task: () -> ()){
|
||
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> <span class="hljs-number">0.</span>.self{
|
||
task()
|
||
}
|
||
}
|
||
}
|
||
</code></pre>
|
||
<p>这个<code>repetitions</code>方法使用了一个<code>() -> ()</code>类型的单参数（single argument），表明函数没有参数而且没有返回值。</p>
|
||
<p>定义该扩展之后，你就可以对任意整数调用<code>repetitions</code>方法,实现的功能则是多次执行某任务：</p>
|
||
<pre><code class="lang-javascript"><span class="hljs-number">3.</span>repetitions({
|
||
println(<span class="hljs-string">"Hello!"</span>)
|
||
})
|
||
<span class="hljs-comment">// Hello!</span>
|
||
<span class="hljs-comment">// Hello!</span>
|
||
<span class="hljs-comment">// Hello!</span>
|
||
</code></pre>
|
||
<p>可以使用trailing闭包使调用更加简洁：</p>
|
||
<pre><code class="lang-javascript"><span class="hljs-number">3.</span>repetitions{
|
||
println(<span class="hljs-string">"Goodbye!"</span>)
|
||
}
|
||
<span class="hljs-comment">// Goodbye!</span>
|
||
<span class="hljs-comment">// Goodbye!</span>
|
||
<span class="hljs-comment">// Goodbye!</span>
|
||
</code></pre>
|
||
<h3 id="-">修改实例方法</h3>
|
||
<p>通过扩展添加的实例方法也可以修改该实例本身。结构体和枚举类型中修改<code>self</code>或其属性的方法必须将该实例方法标注为<code>mutating</code>，正如来自原始实现的修改方法一样。</p>
|
||
<p>下面的例子向Swift的<code>Int</code>类型添加了一个新的名为<code>square</code>的修改方法，来实现一个原始值的平方计算：</p>
|
||
<pre><code class="lang-javascript">extension Int{
|
||
mutating func square(){
|
||
self = self * self
|
||
}
|
||
}
|
||
<span class="hljs-keyword">var</span> someInt = <span class="hljs-number">3</span>
|
||
someInt.square()
|
||
<span class="hljs-comment">// someInt is now 9</span>
|
||
</code></pre>
|
||
<h2 id="-">下标</h2>
|
||
<p>扩展可以向一个已有类型添加新下标。这个例子向Swift内建类型<code>Int</code>添加了一个整型下标。该下标<code>[n]</code>返回十进制数字从右向左数的第n个数字</p>
|
||
<ul>
|
||
<li>123456789[0]返回9</li>
|
||
<li>123456789[1]返回8</li>
|
||
</ul>
|
||
<p>等等</p>
|
||
<pre><code class="lang-javascript">extension Int{
|
||
subscript(digitIndex: Int) -> Int {
|
||
<span class="hljs-keyword">var</span> decimalBase = <span class="hljs-number">1</span>
|
||
<span class="hljs-keyword">for</span> _ <span class="hljs-keyword">in</span> <span class="hljs-number">1.</span>..digitIndex{
|
||
decimalBase *= <span class="hljs-number">10</span>
|
||
}
|
||
<span class="hljs-keyword">return</span> (self / decimalBase) % <span class="hljs-number">10</span>
|
||
}
|
||
}
|
||
<span class="hljs-number">746381295</span>[<span class="hljs-number">0</span>]
|
||
<span class="hljs-comment">// returns 5</span>
|
||
<span class="hljs-number">746381295</span>[<span class="hljs-number">1</span>]
|
||
<span class="hljs-comment">// returns 9</span>
|
||
<span class="hljs-number">746381295</span>[<span class="hljs-number">2</span>]
|
||
<span class="hljs-comment">// returns 2</span>
|
||
<span class="hljs-number">746381295</span>[<span class="hljs-number">8</span>]
|
||
<span class="hljs-comment">// returns 7</span>
|
||
</code></pre>
|
||
<p>如果该<code>Int</code>值没有足够的位数，即下标越界，那么上述实现的下标会返回0，因为它会在数字左边自动补0：</p>
|
||
<pre><code class="lang-javascript"><span class="hljs-number">746381295</span>[<span class="hljs-number">9</span>]
|
||
<span class="hljs-comment">//returns 0, 即等同于：</span>
|
||
<span class="hljs-number">0746381295</span>[<span class="hljs-number">9</span>]
|
||
</code></pre>
|
||
<h2 id="-">嵌套类型</h2>
|
||
<p>扩展可以向已有的类、结构体和枚举添加新的嵌套类型：</p>
|
||
<pre><code class="lang-javascript">extension Character {
|
||
enum Kind {
|
||
<span class="hljs-keyword">case</span> Vowel, Consonant, Other
|
||
}
|
||
<span class="hljs-keyword">var</span> kind: Kind {
|
||
<span class="hljs-keyword">switch</span> <span class="hljs-built_in">String</span>(self).lowercaseString {
|
||
<span class="hljs-keyword">case</span> <span class="hljs-string">"a"</span>, <span class="hljs-string">"e"</span>, <span class="hljs-string">"i"</span>, <span class="hljs-string">"o"</span>, <span class="hljs-string">"u"</span>:
|
||
<span class="hljs-keyword">return</span> .Vowel
|
||
<span class="hljs-keyword">case</span> <span class="hljs-string">"b"</span>, <span class="hljs-string">"c"</span>, <span class="hljs-string">"d"</span>, <span class="hljs-string">"f"</span>, <span class="hljs-string">"g"</span>, <span class="hljs-string">"h"</span>, <span class="hljs-string">"j"</span>, <span class="hljs-string">"k"</span>, <span class="hljs-string">"l"</span>, <span class="hljs-string">"m"</span>,
|
||
<span class="hljs-string">"n"</span>, <span class="hljs-string">"p"</span>, <span class="hljs-string">"q"</span>, <span class="hljs-string">"r"</span>, <span class="hljs-string">"s"</span>, <span class="hljs-string">"t"</span>, <span class="hljs-string">"v"</span>, <span class="hljs-string">"w"</span>, <span class="hljs-string">"x"</span>, <span class="hljs-string">"y"</span>, <span class="hljs-string">"z"</span>:
|
||
<span class="hljs-keyword">return</span> .Consonant
|
||
<span class="hljs-keyword">default</span>:
|
||
<span class="hljs-keyword">return</span> .Other
|
||
}
|
||
}
|
||
}
|
||
</code></pre>
|
||
<p>该例子向<code>Character</code>添加了新的嵌套枚举。这个名为<code>Kind</code>的枚举表示特定字符的类型。具体来说，就是表示一个标准的拉丁脚本中的字符是元音还是辅音（不考虑口语和地方变种），或者是其它类型。</p>
|
||
<p>这个类子还向<code>Character</code>添加了一个新的计算实例属性，即<code>kind</code>，用来返回合适的<code>Kind</code>枚举成员。</p>
|
||
<p>现在，这个嵌套枚举可以和一个<code>Character</code>值联合使用了：</p>
|
||
<pre><code class="lang-javascript">func printLetterKinds(word: <span class="hljs-built_in">String</span>) {
|
||
println(<span class="hljs-string">"'\\(word)' is made up of the following kinds of letters:"</span>)
|
||
<span class="hljs-keyword">for</span> character <span class="hljs-keyword">in</span> word {
|
||
<span class="hljs-keyword">switch</span> character.kind {
|
||
<span class="hljs-keyword">case</span> .Vowel:
|
||
print(<span class="hljs-string">"vowel "</span>)
|
||
<span class="hljs-keyword">case</span> .Consonant:
|
||
print(<span class="hljs-string">"consonant "</span>)
|
||
<span class="hljs-keyword">case</span> .Other:
|
||
print(<span class="hljs-string">"other "</span>)
|
||
}
|
||
}
|
||
print(<span class="hljs-string">"\n"</span>)
|
||
}
|
||
printLetterKinds(<span class="hljs-string">"Hello"</span>)
|
||
<span class="hljs-comment">// 'Hello' is made up of the following kinds of letters:</span>
|
||
<span class="hljs-comment">// consonant vowel consonant consonant vowel</span>
|
||
</code></pre>
|
||
<p>函数<code>printLetterKinds</code>的输入是一个<code>String</code>值并对其字符进行迭代。在每次迭代过程中，考虑当前字符的<code>kind</code>计算属性，并打印出合适的类别描述。所以<code>printLetterKinds</code>就可以用来打印一个完整单词中所有字母的类型，正如上述单词<code>"hello"</code>所展示的。</p>
|
||
<blockquote>
|
||
<p>注意
|
||
由于已知<code>character.kind</code>是<code>Character.Kind</code>型，所以<code>Character.Kind</code>中的所有成员值都可以使用<code>switch</code>语句里的形式简写，比如使用 <code>.Vowel</code>代替<code>Character.Kind.Vowel</code></p>
|
||
</blockquote>
|
||
|
||
|
||
</section>
|
||
|
||
</div>
|
||
</div>
|
||
</div>
|
||
|
||
|
||
<a href="../chapter2/19_Nested_Types.html" class="navigation navigation-prev " aria-label="Previous page: 嵌套类型"><i class="fa fa-angle-left"></i></a>
|
||
|
||
|
||
<a href="../chapter2/21_Protocols.html" class="navigation navigation-next " aria-label="Next page: 协议"><i class="fa fa-angle-right"></i></a>
|
||
|
||
</div>
|
||
</div>
|
||
|
||
|
||
|
||
<script src="http://cdn.bootcss.com/ace/1.1.3/ace.js"></script>
|
||
<script src="http://cdn.bootcss.com/ace/1.1.3/mode-javascript.js"></script>
|
||
<script src="../gitbook/jsrepl/jsrepl.js" id="jsrepl-script"></script>
|
||
<script src="../gitbook/app.js"></script>
|
||
|
||
|
||
|
||
<script src="../gitbook/plugins/gitbook-plugin-mixpanel/plugin.js"></script>
|
||
|
||
|
||
|
||
<script src="http://cdn.mathjax.org/mathjax/2.0-latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>
|
||
|
||
|
||
|
||
<script src="../gitbook/plugins/gitbook-plugin-mathjax/plugin.js"></script>
|
||
|
||
|
||
<script>
|
||
require(["gitbook"], function(gitbook) {
|
||
var config = {};
|
||
gitbook.start(config);
|
||
});
|
||
</script>
|
||
|
||
|
||
</body>
|
||
|
||
</html>
|