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2248 lines
82 KiB
HTML
2248 lines
82 KiB
HTML
<!DOCTYPE HTML>
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<html lang="zh-tw" >
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<head>
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<meta charset="UTF-8">
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<meta http-equiv="X-UA-Compatible" content="IE=edge" />
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<title>Display遞歸打印 | Go语言圣经</title>
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<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
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<meta name="description" content="">
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<meta name="generator" content="GitBook 2.6.6">
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<meta name="HandheldFriendly" content="true"/>
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<meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no">
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<meta name="apple-mobile-web-app-capable" content="yes">
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<meta name="apple-mobile-web-app-status-bar-style" content="black">
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<link rel="apple-touch-icon-precomposed" sizes="152x152" href="../gitbook/images/apple-touch-icon-precomposed-152.png">
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<link rel="shortcut icon" href="../gitbook/images/favicon.ico" type="image/x-icon">
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<link rel="stylesheet" href="../gitbook/style.css">
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<link rel="stylesheet" href="../gitbook/plugins/gitbook-plugin-katex/katex.min.css">
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<link rel="stylesheet" href="../gitbook/plugins/gitbook-plugin-highlight/website.css">
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<link rel="stylesheet" href="../gitbook/plugins/gitbook-plugin-fontsettings/website.css">
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<link rel="next" href="../ch12/ch12-04.html" />
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<link rel="prev" href="../ch12/ch12-02.html" />
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</head>
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<body>
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<div class="book"
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data-level="12.3"
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data-chapter-title="Display遞歸打印"
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data-filepath="ch12/ch12-03.md"
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data-basepath=".."
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data-revision="Sat Jan 02 2016 16:00:23 GMT+0800 (中国标准时间)"
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data-innerlanguage="">
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<div class="book-summary">
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<nav role="navigation">
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<ul class="summary">
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<li class="chapter " data-level="0" data-path="index.html">
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<a href="../index.html">
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<i class="fa fa-check"></i>
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前言
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</a>
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<ul class="articles">
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<li class="chapter " data-level="0.1" data-path="ch0/ch0-01.html">
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<a href="../ch0/ch0-01.html">
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<i class="fa fa-check"></i>
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<b>0.1.</b>
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Go語言起源
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</a>
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</li>
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<li class="chapter " data-level="0.2" data-path="ch0/ch0-02.html">
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<a href="../ch0/ch0-02.html">
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<i class="fa fa-check"></i>
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<b>0.2.</b>
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Go語言項目
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</a>
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</li>
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<li class="chapter " data-level="0.3" data-path="ch0/ch0-03.html">
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<a href="../ch0/ch0-03.html">
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<i class="fa fa-check"></i>
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<b>0.3.</b>
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本書的組織
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</a>
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</li>
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<li class="chapter " data-level="0.4" data-path="ch0/ch0-04.html">
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<a href="../ch0/ch0-04.html">
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<i class="fa fa-check"></i>
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<b>0.4.</b>
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更多的信息
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</a>
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</li>
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<li class="chapter " data-level="0.5" data-path="ch0/ch0-05.html">
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<a href="../ch0/ch0-05.html">
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<i class="fa fa-check"></i>
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<b>0.5.</b>
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致謝
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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="1" data-path="ch1/ch1.html">
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<a href="../ch1/ch1.html">
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<i class="fa fa-check"></i>
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<b>1.</b>
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入門
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</a>
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<ul class="articles">
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<li class="chapter " data-level="1.1" data-path="ch1/ch1-01.html">
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<a href="../ch1/ch1-01.html">
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<i class="fa fa-check"></i>
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<b>1.1.</b>
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Hello, World
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</a>
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</li>
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<li class="chapter " data-level="1.2" data-path="ch1/ch1-02.html">
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<a href="../ch1/ch1-02.html">
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<i class="fa fa-check"></i>
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<b>1.2.</b>
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命令行參數
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</a>
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</li>
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<li class="chapter " data-level="1.3" data-path="ch1/ch1-03.html">
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<a href="../ch1/ch1-03.html">
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<i class="fa fa-check"></i>
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<b>1.3.</b>
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査找重複的行
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</a>
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</li>
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<li class="chapter " data-level="1.4" data-path="ch1/ch1-04.html">
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<a href="../ch1/ch1-04.html">
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<i class="fa fa-check"></i>
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<b>1.4.</b>
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GIF動畵
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</a>
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</li>
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<li class="chapter " data-level="1.5" data-path="ch1/ch1-05.html">
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<a href="../ch1/ch1-05.html">
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<i class="fa fa-check"></i>
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<b>1.5.</b>
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獲取URL
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</a>
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</li>
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<li class="chapter " data-level="1.6" data-path="ch1/ch1-06.html">
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<a href="../ch1/ch1-06.html">
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<i class="fa fa-check"></i>
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<b>1.6.</b>
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併發獲取多個URL
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</a>
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</li>
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<li class="chapter " data-level="1.7" data-path="ch1/ch1-07.html">
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<a href="../ch1/ch1-07.html">
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<i class="fa fa-check"></i>
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<b>1.7.</b>
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Web服務
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</a>
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</li>
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<li class="chapter " data-level="1.8" data-path="ch1/ch1-08.html">
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<a href="../ch1/ch1-08.html">
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<i class="fa fa-check"></i>
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<b>1.8.</b>
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本章要點
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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="2" data-path="ch2/ch2.html">
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<a href="../ch2/ch2.html">
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<i class="fa fa-check"></i>
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<b>2.</b>
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程序結構
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</a>
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<ul class="articles">
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<li class="chapter " data-level="2.1" data-path="ch2/ch2-01.html">
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<a href="../ch2/ch2-01.html">
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<i class="fa fa-check"></i>
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<b>2.1.</b>
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命名
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</a>
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</li>
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<li class="chapter " data-level="2.2" data-path="ch2/ch2-02.html">
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<a href="../ch2/ch2-02.html">
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<i class="fa fa-check"></i>
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<b>2.2.</b>
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聲明
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</a>
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</li>
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<li class="chapter " data-level="2.3" data-path="ch2/ch2-03.html">
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<a href="../ch2/ch2-03.html">
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<i class="fa fa-check"></i>
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<b>2.3.</b>
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變量
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</a>
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</li>
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<li class="chapter " data-level="2.4" data-path="ch2/ch2-04.html">
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<a href="../ch2/ch2-04.html">
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<i class="fa fa-check"></i>
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<b>2.4.</b>
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賦值
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</a>
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</li>
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<li class="chapter " data-level="2.5" data-path="ch2/ch2-05.html">
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<a href="../ch2/ch2-05.html">
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<i class="fa fa-check"></i>
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<b>2.5.</b>
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類型
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</a>
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</li>
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<li class="chapter " data-level="2.6" data-path="ch2/ch2-06.html">
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<a href="../ch2/ch2-06.html">
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<i class="fa fa-check"></i>
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<b>2.6.</b>
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包和文件
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</a>
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</li>
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<li class="chapter " data-level="2.7" data-path="ch2/ch2-07.html">
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<a href="../ch2/ch2-07.html">
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<i class="fa fa-check"></i>
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<b>2.7.</b>
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作用域
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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="ch3/ch3.html">
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<a href="../ch3/ch3.html">
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<i class="fa fa-check"></i>
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<b>3.</b>
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基礎數據類型
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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="ch3/ch3-01.html">
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<a href="../ch3/ch3-01.html">
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<i class="fa fa-check"></i>
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<b>3.1.</b>
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整型
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</a>
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</li>
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<li class="chapter " data-level="3.2" data-path="ch3/ch3-02.html">
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<a href="../ch3/ch3-02.html">
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<i class="fa fa-check"></i>
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<b>3.2.</b>
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浮點數
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</a>
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</li>
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<li class="chapter " data-level="3.3" data-path="ch3/ch3-03.html">
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<a href="../ch3/ch3-03.html">
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<i class="fa fa-check"></i>
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<b>3.3.</b>
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複數
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</a>
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</li>
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<li class="chapter " data-level="3.4" data-path="ch3/ch3-04.html">
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<a href="../ch3/ch3-04.html">
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<i class="fa fa-check"></i>
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<b>3.4.</b>
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布爾型
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</a>
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</li>
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<li class="chapter " data-level="3.5" data-path="ch3/ch3-05.html">
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<a href="../ch3/ch3-05.html">
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<i class="fa fa-check"></i>
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<b>3.5.</b>
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字符串
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</a>
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</li>
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<li class="chapter " data-level="3.6" data-path="ch3/ch3-06.html">
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<a href="../ch3/ch3-06.html">
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<i class="fa fa-check"></i>
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<b>3.6.</b>
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常量
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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="4" data-path="ch4/ch4.html">
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<a href="../ch4/ch4.html">
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<i class="fa fa-check"></i>
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<b>4.</b>
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複合數據類型
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</a>
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<ul class="articles">
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<li class="chapter " data-level="4.1" data-path="ch4/ch4-01.html">
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<a href="../ch4/ch4-01.html">
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<i class="fa fa-check"></i>
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<b>4.1.</b>
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數組
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</a>
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</li>
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<li class="chapter " data-level="4.2" data-path="ch4/ch4-02.html">
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<a href="../ch4/ch4-02.html">
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<i class="fa fa-check"></i>
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<b>4.2.</b>
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Slice
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</a>
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</li>
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<li class="chapter " data-level="4.3" data-path="ch4/ch4-03.html">
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<a href="../ch4/ch4-03.html">
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<i class="fa fa-check"></i>
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<b>4.3.</b>
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Map
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</a>
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</li>
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<li class="chapter " data-level="4.4" data-path="ch4/ch4-04.html">
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<a href="../ch4/ch4-04.html">
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<i class="fa fa-check"></i>
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<b>4.4.</b>
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結構體
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</a>
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</li>
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<li class="chapter " data-level="4.5" data-path="ch4/ch4-05.html">
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<a href="../ch4/ch4-05.html">
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<i class="fa fa-check"></i>
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<b>4.5.</b>
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JSON
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</a>
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</li>
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<li class="chapter " data-level="4.6" data-path="ch4/ch4-06.html">
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<a href="../ch4/ch4-06.html">
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<i class="fa fa-check"></i>
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<b>4.6.</b>
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文本和HTML模闆
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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="5" data-path="ch5/ch5.html">
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<a href="../ch5/ch5.html">
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<i class="fa fa-check"></i>
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<b>5.</b>
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函數
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</a>
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<ul class="articles">
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<li class="chapter " data-level="5.1" data-path="ch5/ch5-01.html">
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<a href="../ch5/ch5-01.html">
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<i class="fa fa-check"></i>
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<b>5.1.</b>
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函數聲明
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</a>
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</li>
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<li class="chapter " data-level="5.2" data-path="ch5/ch5-02.html">
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|
|
|
|
<a href="../ch5/ch5-02.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>5.2.</b>
|
|
|
|
遞歸
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="5.3" data-path="ch5/ch5-03.html">
|
|
|
|
|
|
<a href="../ch5/ch5-03.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>5.3.</b>
|
|
|
|
多返迴值
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="5.4" data-path="ch5/ch5-04.html">
|
|
|
|
|
|
<a href="../ch5/ch5-04.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>5.4.</b>
|
|
|
|
錯誤
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="5.5" data-path="ch5/ch5-05.html">
|
|
|
|
|
|
<a href="../ch5/ch5-05.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>5.5.</b>
|
|
|
|
函數值
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="5.6" data-path="ch5/ch5-06.html">
|
|
|
|
|
|
<a href="../ch5/ch5-06.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>5.6.</b>
|
|
|
|
匿名函數
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="5.7" data-path="ch5/ch5-07.html">
|
|
|
|
|
|
<a href="../ch5/ch5-07.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>5.7.</b>
|
|
|
|
可變參數
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="5.8" data-path="ch5/ch5-08.html">
|
|
|
|
|
|
<a href="../ch5/ch5-08.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>5.8.</b>
|
|
|
|
Deferred函數
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="5.9" data-path="ch5/ch5-09.html">
|
|
|
|
|
|
<a href="../ch5/ch5-09.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>5.9.</b>
|
|
|
|
Panic異常
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="5.10" data-path="ch5/ch5-10.html">
|
|
|
|
|
|
<a href="../ch5/ch5-10.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>5.10.</b>
|
|
|
|
Recover捕獲異常
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
|
|
</ul>
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="6" data-path="ch6/ch6.html">
|
|
|
|
|
|
<a href="../ch6/ch6.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>6.</b>
|
|
|
|
方法
|
|
</a>
|
|
|
|
|
|
<ul class="articles">
|
|
|
|
|
|
<li class="chapter " data-level="6.1" data-path="ch6/ch6-01.html">
|
|
|
|
|
|
<a href="../ch6/ch6-01.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>6.1.</b>
|
|
|
|
方法聲明
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="6.2" data-path="ch6/ch6-02.html">
|
|
|
|
|
|
<a href="../ch6/ch6-02.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>6.2.</b>
|
|
|
|
基於指針對象的方法
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="6.3" data-path="ch6/ch6-03.html">
|
|
|
|
|
|
<a href="../ch6/ch6-03.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>6.3.</b>
|
|
|
|
通過嵌入結構體來擴展類型
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="6.4" data-path="ch6/ch6-04.html">
|
|
|
|
|
|
<a href="../ch6/ch6-04.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>6.4.</b>
|
|
|
|
方法值和方法表達式
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="6.5" data-path="ch6/ch6-05.html">
|
|
|
|
|
|
<a href="../ch6/ch6-05.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>6.5.</b>
|
|
|
|
示例: Bit數組
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="6.6" data-path="ch6/ch6-06.html">
|
|
|
|
|
|
<a href="../ch6/ch6-06.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>6.6.</b>
|
|
|
|
封裝
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
|
|
</ul>
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="7" data-path="ch7/ch7.html">
|
|
|
|
|
|
<a href="../ch7/ch7.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>7.</b>
|
|
|
|
接口
|
|
</a>
|
|
|
|
|
|
<ul class="articles">
|
|
|
|
|
|
<li class="chapter " data-level="7.1" data-path="ch7/ch7-01.html">
|
|
|
|
|
|
<a href="../ch7/ch7-01.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>7.1.</b>
|
|
|
|
接口是合約
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="7.2" data-path="ch7/ch7-02.html">
|
|
|
|
|
|
<a href="../ch7/ch7-02.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>7.2.</b>
|
|
|
|
接口類型
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="7.3" data-path="ch7/ch7-03.html">
|
|
|
|
|
|
<a href="../ch7/ch7-03.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>7.3.</b>
|
|
|
|
實現接口的條件
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="7.4" data-path="ch7/ch7-04.html">
|
|
|
|
|
|
<a href="../ch7/ch7-04.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>7.4.</b>
|
|
|
|
flag.Value接口
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="7.5" data-path="ch7/ch7-05.html">
|
|
|
|
|
|
<a href="../ch7/ch7-05.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>7.5.</b>
|
|
|
|
接口值
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="7.6" data-path="ch7/ch7-06.html">
|
|
|
|
|
|
<a href="../ch7/ch7-06.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>7.6.</b>
|
|
|
|
sort.Interface接口
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="7.7" data-path="ch7/ch7-07.html">
|
|
|
|
|
|
<a href="../ch7/ch7-07.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>7.7.</b>
|
|
|
|
http.Handler接口
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="7.8" data-path="ch7/ch7-08.html">
|
|
|
|
|
|
<a href="../ch7/ch7-08.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>7.8.</b>
|
|
|
|
error接口
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="7.9" data-path="ch7/ch7-09.html">
|
|
|
|
|
|
<a href="../ch7/ch7-09.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>7.9.</b>
|
|
|
|
示例: 表達式求值
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="7.10" data-path="ch7/ch7-10.html">
|
|
|
|
|
|
<a href="../ch7/ch7-10.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>7.10.</b>
|
|
|
|
類型斷言
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="7.11" data-path="ch7/ch7-11.html">
|
|
|
|
|
|
<a href="../ch7/ch7-11.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>7.11.</b>
|
|
|
|
基於類型斷言識别錯誤類型
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="7.12" data-path="ch7/ch7-12.html">
|
|
|
|
|
|
<a href="../ch7/ch7-12.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>7.12.</b>
|
|
|
|
通過類型斷言査詢接口
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="7.13" data-path="ch7/ch7-13.html">
|
|
|
|
|
|
<a href="../ch7/ch7-13.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>7.13.</b>
|
|
|
|
類型分支
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="7.14" data-path="ch7/ch7-14.html">
|
|
|
|
|
|
<a href="../ch7/ch7-14.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>7.14.</b>
|
|
|
|
示例: 基於標記的XML解碼
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="7.15" data-path="ch7/ch7-15.html">
|
|
|
|
|
|
<a href="../ch7/ch7-15.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>7.15.</b>
|
|
|
|
補充幾點
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
|
|
</ul>
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="8" data-path="ch8/ch8.html">
|
|
|
|
|
|
<a href="../ch8/ch8.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>8.</b>
|
|
|
|
Goroutines和Channels
|
|
</a>
|
|
|
|
|
|
<ul class="articles">
|
|
|
|
|
|
<li class="chapter " data-level="8.1" data-path="ch8/ch8-01.html">
|
|
|
|
|
|
<a href="../ch8/ch8-01.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>8.1.</b>
|
|
|
|
Goroutines
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="8.2" data-path="ch8/ch8-02.html">
|
|
|
|
|
|
<a href="../ch8/ch8-02.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>8.2.</b>
|
|
|
|
示例: 併發的Clock服務
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="8.3" data-path="ch8/ch8-03.html">
|
|
|
|
|
|
<a href="../ch8/ch8-03.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>8.3.</b>
|
|
|
|
示例: 併發的Echo服務
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="8.4" data-path="ch8/ch8-04.html">
|
|
|
|
|
|
<a href="../ch8/ch8-04.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>8.4.</b>
|
|
|
|
Channels
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="8.5" data-path="ch8/ch8-05.html">
|
|
|
|
|
|
<a href="../ch8/ch8-05.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>8.5.</b>
|
|
|
|
併行的循環
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="8.6" data-path="ch8/ch8-06.html">
|
|
|
|
|
|
<a href="../ch8/ch8-06.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>8.6.</b>
|
|
|
|
示例: 併發的Web爬蟲
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="8.7" data-path="ch8/ch8-07.html">
|
|
|
|
|
|
<a href="../ch8/ch8-07.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>8.7.</b>
|
|
|
|
基於select的多路複用
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="8.8" data-path="ch8/ch8-08.html">
|
|
|
|
|
|
<a href="../ch8/ch8-08.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>8.8.</b>
|
|
|
|
示例: 併發的字典遍歷
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="8.9" data-path="ch8/ch8-09.html">
|
|
|
|
|
|
<a href="../ch8/ch8-09.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>8.9.</b>
|
|
|
|
併發的退出
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="8.10" data-path="ch8/ch8-10.html">
|
|
|
|
|
|
<a href="../ch8/ch8-10.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>8.10.</b>
|
|
|
|
示例: 聊天服務
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
|
|
</ul>
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="9" data-path="ch9/ch9.html">
|
|
|
|
|
|
<a href="../ch9/ch9.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>9.</b>
|
|
|
|
基於共享變量的併發
|
|
</a>
|
|
|
|
|
|
<ul class="articles">
|
|
|
|
|
|
<li class="chapter " data-level="9.1" data-path="ch9/ch9-01.html">
|
|
|
|
|
|
<a href="../ch9/ch9-01.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>9.1.</b>
|
|
|
|
競爭條件
|
|
</a>
|
|
|
|
|
|
</li>
|
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|
|
<li class="chapter " data-level="9.2" data-path="ch9/ch9-02.html">
|
|
|
|
|
|
<a href="../ch9/ch9-02.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>9.2.</b>
|
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|
|
sync.Mutex互斥鎖
|
|
</a>
|
|
|
|
|
|
</li>
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|
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<li class="chapter " data-level="9.3" data-path="ch9/ch9-03.html">
|
|
|
|
|
|
<a href="../ch9/ch9-03.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
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<b>9.3.</b>
|
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sync.RWMutex讀寫鎖
|
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</a>
|
|
|
|
|
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</li>
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<li class="chapter " data-level="9.4" data-path="ch9/ch9-04.html">
|
|
|
|
|
|
<a href="../ch9/ch9-04.html">
|
|
|
|
<i class="fa fa-check"></i>
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<b>9.4.</b>
|
|
|
|
內存同步
|
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</a>
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</li>
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<li class="chapter " data-level="9.5" data-path="ch9/ch9-05.html">
|
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|
|
<a href="../ch9/ch9-05.html">
|
|
|
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<i class="fa fa-check"></i>
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<b>9.5.</b>
|
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|
sync.Once初始化
|
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</a>
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</li>
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<li class="chapter " data-level="9.6" data-path="ch9/ch9-06.html">
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|
|
|
|
<a href="../ch9/ch9-06.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
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<b>9.6.</b>
|
|
|
|
競爭條件檢測
|
|
</a>
|
|
|
|
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</li>
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|
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<li class="chapter " data-level="9.7" data-path="ch9/ch9-07.html">
|
|
|
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|
|
<a href="../ch9/ch9-07.html">
|
|
|
|
<i class="fa fa-check"></i>
|
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<b>9.7.</b>
|
|
|
|
示例: 併發的非阻塞緩存
|
|
</a>
|
|
|
|
|
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</li>
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|
|
<li class="chapter " data-level="9.8" data-path="ch9/ch9-08.html">
|
|
|
|
|
|
<a href="../ch9/ch9-08.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
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<b>9.8.</b>
|
|
|
|
Goroutines和線程
|
|
</a>
|
|
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</li>
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|
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</ul>
|
|
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</li>
|
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|
|
<li class="chapter " data-level="10" data-path="ch10/ch10.html">
|
|
|
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|
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<a href="../ch10/ch10.html">
|
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|
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<i class="fa fa-check"></i>
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<b>10.</b>
|
|
|
|
包和工具
|
|
</a>
|
|
|
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|
|
<ul class="articles">
|
|
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|
|
<li class="chapter " data-level="10.1" data-path="ch10/ch10-01.html">
|
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<a href="../ch10/ch10-01.html">
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<i class="fa fa-check"></i>
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<b>10.1.</b>
|
|
|
|
簡介
|
|
</a>
|
|
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|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="10.2" data-path="ch10/ch10-02.html">
|
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<a href="../ch10/ch10-02.html">
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<i class="fa fa-check"></i>
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<b>10.2.</b>
|
|
|
|
導入路徑
|
|
</a>
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</li>
|
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|
|
<li class="chapter " data-level="10.3" data-path="ch10/ch10-03.html">
|
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|
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|
|
<a href="../ch10/ch10-03.html">
|
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|
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<i class="fa fa-check"></i>
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<b>10.3.</b>
|
|
|
|
包聲明
|
|
</a>
|
|
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|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="10.4" data-path="ch10/ch10-04.html">
|
|
|
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|
|
<a href="../ch10/ch10-04.html">
|
|
|
|
<i class="fa fa-check"></i>
|
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<b>10.4.</b>
|
|
|
|
導入聲明
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="10.5" data-path="ch10/ch10-05.html">
|
|
|
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|
|
<a href="../ch10/ch10-05.html">
|
|
|
|
<i class="fa fa-check"></i>
|
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<b>10.5.</b>
|
|
|
|
匿名導入
|
|
</a>
|
|
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|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="10.6" data-path="ch10/ch10-06.html">
|
|
|
|
|
|
<a href="../ch10/ch10-06.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>10.6.</b>
|
|
|
|
包和命名
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="10.7" data-path="ch10/ch10-07.html">
|
|
|
|
|
|
<a href="../ch10/ch10-07.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>10.7.</b>
|
|
|
|
工具
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
|
|
</ul>
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="11" data-path="ch11/ch11.html">
|
|
|
|
|
|
<a href="../ch11/ch11.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>11.</b>
|
|
|
|
測試
|
|
</a>
|
|
|
|
|
|
<ul class="articles">
|
|
|
|
|
|
<li class="chapter " data-level="11.1" data-path="ch11/ch11-01.html">
|
|
|
|
|
|
<a href="../ch11/ch11-01.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>11.1.</b>
|
|
|
|
go test
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="11.2" data-path="ch11/ch11-02.html">
|
|
|
|
|
|
<a href="../ch11/ch11-02.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>11.2.</b>
|
|
|
|
測試函數
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="11.3" data-path="ch11/ch11-03.html">
|
|
|
|
|
|
<a href="../ch11/ch11-03.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>11.3.</b>
|
|
|
|
測試覆蓋率
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="11.4" data-path="ch11/ch11-04.html">
|
|
|
|
|
|
<a href="../ch11/ch11-04.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>11.4.</b>
|
|
|
|
基準測試
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="11.5" data-path="ch11/ch11-05.html">
|
|
|
|
|
|
<a href="../ch11/ch11-05.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>11.5.</b>
|
|
|
|
剖析
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="11.6" data-path="ch11/ch11-06.html">
|
|
|
|
|
|
<a href="../ch11/ch11-06.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>11.6.</b>
|
|
|
|
示例函數
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
|
|
</ul>
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="12" data-path="ch12/ch12.html">
|
|
|
|
|
|
<a href="../ch12/ch12.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>12.</b>
|
|
|
|
反射
|
|
</a>
|
|
|
|
|
|
<ul class="articles">
|
|
|
|
|
|
<li class="chapter " data-level="12.1" data-path="ch12/ch12-01.html">
|
|
|
|
|
|
<a href="../ch12/ch12-01.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>12.1.</b>
|
|
|
|
爲何需要反射?
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="12.2" data-path="ch12/ch12-02.html">
|
|
|
|
|
|
<a href="../ch12/ch12-02.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>12.2.</b>
|
|
|
|
reflect.Type和reflect.Value
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter active" data-level="12.3" data-path="ch12/ch12-03.html">
|
|
|
|
|
|
<a href="../ch12/ch12-03.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>12.3.</b>
|
|
|
|
Display遞歸打印
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="12.4" data-path="ch12/ch12-04.html">
|
|
|
|
|
|
<a href="../ch12/ch12-04.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>12.4.</b>
|
|
|
|
示例: 編碼S表達式
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="12.5" data-path="ch12/ch12-05.html">
|
|
|
|
|
|
<a href="../ch12/ch12-05.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>12.5.</b>
|
|
|
|
通過reflect.Value脩改值
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="12.6" data-path="ch12/ch12-06.html">
|
|
|
|
|
|
<a href="../ch12/ch12-06.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>12.6.</b>
|
|
|
|
示例: 解碼S表達式
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="12.7" data-path="ch12/ch12-07.html">
|
|
|
|
|
|
<a href="../ch12/ch12-07.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>12.7.</b>
|
|
|
|
獲取結構體字段標識
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="12.8" data-path="ch12/ch12-08.html">
|
|
|
|
|
|
<a href="../ch12/ch12-08.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>12.8.</b>
|
|
|
|
顯示一個類型的方法集
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="12.9" data-path="ch12/ch12-09.html">
|
|
|
|
|
|
<a href="../ch12/ch12-09.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>12.9.</b>
|
|
|
|
幾點忠告
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
|
|
</ul>
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="13" data-path="ch13/ch13.html">
|
|
|
|
|
|
<a href="../ch13/ch13.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>13.</b>
|
|
|
|
底層編程
|
|
</a>
|
|
|
|
|
|
<ul class="articles">
|
|
|
|
|
|
<li class="chapter " data-level="13.1" data-path="ch13/ch13-01.html">
|
|
|
|
|
|
<a href="../ch13/ch13-01.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>13.1.</b>
|
|
|
|
unsafe.Sizeof, Alignof 和 Offsetof
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="13.2" data-path="ch13/ch13-02.html">
|
|
|
|
|
|
<a href="../ch13/ch13-02.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>13.2.</b>
|
|
|
|
unsafe.Pointer
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="13.3" data-path="ch13/ch13-03.html">
|
|
|
|
|
|
<a href="../ch13/ch13-03.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>13.3.</b>
|
|
|
|
示例: 深度相等判斷
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="13.4" data-path="ch13/ch13-04.html">
|
|
|
|
|
|
<a href="../ch13/ch13-04.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>13.4.</b>
|
|
|
|
通過cgo調用C代碼
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="13.5" data-path="ch13/ch13-05.html">
|
|
|
|
|
|
<a href="../ch13/ch13-05.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>13.5.</b>
|
|
|
|
幾點忠告
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
|
|
</ul>
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="14" data-path="CONTRIBUTORS.html">
|
|
|
|
|
|
<a href="../CONTRIBUTORS.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>14.</b>
|
|
|
|
附録
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
|
|
|
|
|
|
<li class="divider"></li>
|
|
<li>
|
|
<a href="https://www.gitbook.com" target="blank" class="gitbook-link">
|
|
本書使用 GitBook 釋出
|
|
</a>
|
|
</li>
|
|
|
|
</ul>
|
|
</nav>
|
|
</div>
|
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|
|
<div class="book-body">
|
|
<div class="body-inner">
|
|
<div class="book-header" role="navigation">
|
|
<!-- Actions Left -->
|
|
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|
|
<!-- Title -->
|
|
<h1>
|
|
<i class="fa fa-circle-o-notch fa-spin"></i>
|
|
<a href="../" >Go语言圣经</a>
|
|
</h1>
|
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</div>
|
|
|
|
<div class="page-wrapper" tabindex="-1" role="main">
|
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<div class="page-inner">
|
|
|
|
|
|
<section class="normal" id="section-">
|
|
|
|
<h2 id="123-display遞歸打印">12.3. Display遞歸打印</h2>
|
|
<p>接下來，讓我們看看如何改善聚合數據類型的顯示。我們併不想完全剋隆一個fmt.Sprint函數，我們隻是像構建一個用於調式用的Display函數，給定一個聚合類型x，打印這個值對應的完整的結構，同時記録每個發現的每個元素的路徑。讓我們從一個例子開始。</p>
|
|
<pre><code class="lang-Go">e, _ := eval.Parse(<span class="hljs-string">"sqrt(A / pi)"</span>)
|
|
Display(<span class="hljs-string">"e"</span>, e)
|
|
</code></pre>
|
|
<p>在上面的調用中，傳入Display函數的參數是在7.9節一個表達式求值函數返迴的語法樹。Display函數的輸出如下：</p>
|
|
<pre><code class="lang-Go">Display e (eval.call):
|
|
e.fn = <span class="hljs-string">"sqrt"</span>
|
|
e.args[<span class="hljs-number">0</span>].<span class="hljs-keyword">type</span> = eval.binary
|
|
e.args[<span class="hljs-number">0</span>].value.op = <span class="hljs-number">47</span>
|
|
e.args[<span class="hljs-number">0</span>].value.x.<span class="hljs-keyword">type</span> = eval.Var
|
|
e.args[<span class="hljs-number">0</span>].value.x.value = <span class="hljs-string">"A"</span>
|
|
e.args[<span class="hljs-number">0</span>].value.y.<span class="hljs-keyword">type</span> = eval.Var
|
|
e.args[<span class="hljs-number">0</span>].value.y.value = <span class="hljs-string">"pi"</span>
|
|
</code></pre>
|
|
<p>在可能的情況下，你應該避免在一個包中暴露和反射相關的接口。我們將定義一個未導出的display函數用於遞歸處理工作，導出的是Display函數，它隻是display函數簡單的包裝以接受interface{}類型的參數：</p>
|
|
<pre><code class="lang-Go">gopl.io/ch12/display
|
|
|
|
<span class="hljs-keyword">func</span> Display(name <span class="hljs-typename">string</span>, x <span class="hljs-keyword">interface</span>{}) {
|
|
fmt.Printf(<span class="hljs-string">"Display %s (%T):\n"</span>, name, x)
|
|
display(name, reflect.ValueOf(x))
|
|
}
|
|
</code></pre>
|
|
<p>在display函數中，我們使用了前面定義的打印基礎類型——基本類型、函數和chan等——元素值的formatAtom函數，但是我們會使用reflect.Value的方法來遞歸顯示聚合類型的每一個成員或元素。在遞歸下降過程中，path字符串，從最開始傳入的起始值（這里是“e”），將逐步增長以表示如何達到當前值（例如“e.args[0].value”）。</p>
|
|
<p>因爲我們不再模擬fmt.Sprint函數，我們將直接使用fmt包來簡化我們的例子實現。</p>
|
|
<pre><code class="lang-Go"><span class="hljs-keyword">func</span> display(path <span class="hljs-typename">string</span>, v reflect.Value) {
|
|
<span class="hljs-keyword">switch</span> v.Kind() {
|
|
<span class="hljs-keyword">case</span> reflect.Invalid:
|
|
fmt.Printf(<span class="hljs-string">"%s = invalid\n"</span>, path)
|
|
<span class="hljs-keyword">case</span> reflect.Slice, reflect.Array:
|
|
<span class="hljs-keyword">for</span> i := <span class="hljs-number">0</span>; i < v.Len(); i++ {
|
|
display(fmt.Sprintf(<span class="hljs-string">"%s[%d]"</span>, path, i), v.Index(i))
|
|
}
|
|
<span class="hljs-keyword">case</span> reflect.Struct:
|
|
<span class="hljs-keyword">for</span> i := <span class="hljs-number">0</span>; i < v.NumField(); i++ {
|
|
fieldPath := fmt.Sprintf(<span class="hljs-string">"%s.%s"</span>, path, v.Type().Field(i).Name)
|
|
display(fieldPath, v.Field(i))
|
|
}
|
|
<span class="hljs-keyword">case</span> reflect.Map:
|
|
<span class="hljs-keyword">for</span> _, key := <span class="hljs-keyword">range</span> v.MapKeys() {
|
|
display(fmt.Sprintf(<span class="hljs-string">"%s[%s]"</span>, path,
|
|
formatAtom(key)), v.MapIndex(key))
|
|
}
|
|
<span class="hljs-keyword">case</span> reflect.Ptr:
|
|
<span class="hljs-keyword">if</span> v.IsNil() {
|
|
fmt.Printf(<span class="hljs-string">"%s = nil\n"</span>, path)
|
|
} <span class="hljs-keyword">else</span> {
|
|
display(fmt.Sprintf(<span class="hljs-string">"(*%s)"</span>, path), v.Elem())
|
|
}
|
|
<span class="hljs-keyword">case</span> reflect.Interface:
|
|
<span class="hljs-keyword">if</span> v.IsNil() {
|
|
fmt.Printf(<span class="hljs-string">"%s = nil\n"</span>, path)
|
|
} <span class="hljs-keyword">else</span> {
|
|
fmt.Printf(<span class="hljs-string">"%s.type = %s\n"</span>, path, v.Elem().Type())
|
|
display(path+<span class="hljs-string">".value"</span>, v.Elem())
|
|
}
|
|
<span class="hljs-keyword">default</span>: <span class="hljs-comment">// basic types, channels, funcs</span>
|
|
fmt.Printf(<span class="hljs-string">"%s = %s\n"</span>, path, formatAtom(v))
|
|
}
|
|
}
|
|
</code></pre>
|
|
<p>讓我們針對不同類型分别討論。</p>
|
|
<p><strong>Slice和數組：</strong> 兩種的處理邏輯是一樣的。Len方法返迴slice或數組值中的元素個數，Index(i)活動索引i對應的元素，返迴的也是一個reflect.Value類型的值；如果索引i超出范圍的話將導致panic異常，這些行爲和數組或slice類型內建的len(a)和a[i]等操作類似。display針對序列中的每個元素遞歸調用自身處理，我們通過在遞歸處理時向path附加“[i]”來表示訪問路徑。</p>
|
|
<p>雖然reflect.Value類型帶有很多方法，但是隻有少數的方法對任意值都是可以安全調用的。例如，Index方法隻能對Slice、數組或字符串類型的值調用，其它類型如果調用將導致panic異常。</p>
|
|
<p><strong>結構體：</strong> NumField方法報告結構體中成員的數量，Field(i)以reflect.Value類型返迴第i個成員的值。成員列表包含了匿名成員在內的全部成員。通過在path添加“.f”來表示成員路徑，我們必鬚獲得結構體對應的reflect.Type類型信息，包含結構體類型和第i個成員的名字。</p>
|
|
<p><strong>Maps:</strong> MapKeys方法返迴一個reflect.Value類型的slice，每一個都對應map的可以。和往常一樣，遍歷map時順序是隨機的。MapIndex(key)返迴map中key對應的value。我們向path添加“[key]”來表示訪問路徑。（我們這里有一個未完成的工作。其實map的key的類型併不局限於formatAtom能完美處理的類型；數組、結構體和接口都可以作爲map的key。針對這種類型，完善key的顯示信息是練習12.1的任務。）</p>
|
|
<p><strong>指針：</strong> Elem方法返迴指針指向的變量，還是reflect.Value類型。技術指針是nil，這個操作也是安全的，在這種情況下指針是Invalid無效類型，但是我們可以用IsNil方法來顯式地測試一個空指針，這樣我們可以打印更合適的信息。我們在path前面添加“*”，併用括弧包含以避免歧義。</p>
|
|
<p><strong>接口：</strong> 再一次，我們使用IsNil方法來測試接口是否是nil，如果不是，我們可以調用v.Elem()來獲取接口對應的動態值，併且打印對應的類型和值。</p>
|
|
<p>現在我們的Display函數總算完工了，讓我們看看它的表現吧。下面的Movie類型是在4.5節的電影類型上演變來的：</p>
|
|
<pre><code class="lang-Go"><span class="hljs-keyword">type</span> Movie <span class="hljs-keyword">struct</span> {
|
|
Title, Subtitle <span class="hljs-typename">string</span>
|
|
Year <span class="hljs-typename">int</span>
|
|
Color <span class="hljs-typename">bool</span>
|
|
Actor <span class="hljs-keyword">map</span>[<span class="hljs-typename">string</span>]<span class="hljs-typename">string</span>
|
|
Oscars []<span class="hljs-typename">string</span>
|
|
Sequel *<span class="hljs-typename">string</span>
|
|
}
|
|
</code></pre>
|
|
<p>讓我們聲明一個該類型的變量，然後看看Display函數如何顯示它：</p>
|
|
<pre><code class="lang-Go">strangelove := Movie{
|
|
Title: <span class="hljs-string">"Dr. Strangelove"</span>,
|
|
Subtitle: <span class="hljs-string">"How I Learned to Stop Worrying and Love the Bomb"</span>,
|
|
Year: <span class="hljs-number">1964</span>,
|
|
Color: <span class="hljs-constant">false</span>,
|
|
Actor: <span class="hljs-keyword">map</span>[<span class="hljs-typename">string</span>]<span class="hljs-typename">string</span>{
|
|
<span class="hljs-string">"Dr. Strangelove"</span>: <span class="hljs-string">"Peter Sellers"</span>,
|
|
<span class="hljs-string">"Grp. Capt. Lionel Mandrake"</span>: <span class="hljs-string">"Peter Sellers"</span>,
|
|
<span class="hljs-string">"Pres. Merkin Muffley"</span>: <span class="hljs-string">"Peter Sellers"</span>,
|
|
<span class="hljs-string">"Gen. Buck Turgidson"</span>: <span class="hljs-string">"George C. Scott"</span>,
|
|
<span class="hljs-string">"Brig. Gen. Jack D. Ripper"</span>: <span class="hljs-string">"Sterling Hayden"</span>,
|
|
<span class="hljs-string">`Maj. T.J. "King" Kong`</span>: <span class="hljs-string">"Slim Pickens"</span>,
|
|
},
|
|
|
|
Oscars: []<span class="hljs-typename">string</span>{
|
|
<span class="hljs-string">"Best Actor (Nomin.)"</span>,
|
|
<span class="hljs-string">"Best Adapted Screenplay (Nomin.)"</span>,
|
|
<span class="hljs-string">"Best Director (Nomin.)"</span>,
|
|
<span class="hljs-string">"Best Picture (Nomin.)"</span>,
|
|
},
|
|
}
|
|
</code></pre>
|
|
<p>Display("strangelove", strangelove)調用將顯示（strangelove電影對應的中文名是《奇愛博士》）：</p>
|
|
<pre><code class="lang-Go">Display strangelove (display.Movie):
|
|
strangelove.Title = <span class="hljs-string">"Dr. Strangelove"</span>
|
|
strangelove.Subtitle = <span class="hljs-string">"How I Learned to Stop Worrying and Love the Bomb"</span>
|
|
strangelove.Year = <span class="hljs-number">1964</span>
|
|
strangelove.Color = <span class="hljs-constant">false</span>
|
|
strangelove.Actor[<span class="hljs-string">"Gen. Buck Turgidson"</span>] = <span class="hljs-string">"George C. Scott"</span>
|
|
strangelove.Actor[<span class="hljs-string">"Brig. Gen. Jack D. Ripper"</span>] = <span class="hljs-string">"Sterling Hayden"</span>
|
|
strangelove.Actor[<span class="hljs-string">"Maj. T.J. \"King\" Kong"</span>] = <span class="hljs-string">"Slim Pickens"</span>
|
|
strangelove.Actor[<span class="hljs-string">"Dr. Strangelove"</span>] = <span class="hljs-string">"Peter Sellers"</span>
|
|
strangelove.Actor[<span class="hljs-string">"Grp. Capt. Lionel Mandrake"</span>] = <span class="hljs-string">"Peter Sellers"</span>
|
|
strangelove.Actor[<span class="hljs-string">"Pres. Merkin Muffley"</span>] = <span class="hljs-string">"Peter Sellers"</span>
|
|
strangelove.Oscars[<span class="hljs-number">0</span>] = <span class="hljs-string">"Best Actor (Nomin.)"</span>
|
|
strangelove.Oscars[<span class="hljs-number">1</span>] = <span class="hljs-string">"Best Adapted Screenplay (Nomin.)"</span>
|
|
strangelove.Oscars[<span class="hljs-number">2</span>] = <span class="hljs-string">"Best Director (Nomin.)"</span>
|
|
strangelove.Oscars[<span class="hljs-number">3</span>] = <span class="hljs-string">"Best Picture (Nomin.)"</span>
|
|
strangelove.Sequel = <span class="hljs-constant">nil</span>
|
|
</code></pre>
|
|
<p>我們也可以使用Display函數來顯示標準庫中類型的內部結構，例如<code>*os.File</code>類型：</p>
|
|
<pre><code class="lang-Go">Display(<span class="hljs-string">"os.Stderr"</span>, os.Stderr)
|
|
<span class="hljs-comment">// Output:</span>
|
|
<span class="hljs-comment">// Display os.Stderr (*os.File):</span>
|
|
<span class="hljs-comment">// (*(*os.Stderr).file).fd = 2</span>
|
|
<span class="hljs-comment">// (*(*os.Stderr).file).name = "/dev/stderr"</span>
|
|
<span class="hljs-comment">// (*(*os.Stderr).file).nepipe = 0</span>
|
|
</code></pre>
|
|
<p>要註意的是，結構體中未導出的成員對反射也是可見的。需要當心的是這個例子的輸出在不同操作繫統上可能是不同的，併且隨着標準庫的發展也可能導致結果不同。（這也是將這些成員定義爲私有成員的原因之一！）我們深圳可以用Display函數來顯示reflect.Value，來査看<code>*os.File</code>類型的內部表示方式。<code>Display("rV", reflect.ValueOf(os.Stderr))</code>調用的輸出如下，當然不同環境得到的結果可能有差異：</p>
|
|
<pre><code class="lang-Go">Display rV (reflect.Value):
|
|
(*rV.typ).size = <span class="hljs-number">8</span>
|
|
(*rV.typ).hash = <span class="hljs-number">871609668</span>
|
|
(*rV.typ).align = <span class="hljs-number">8</span>
|
|
(*rV.typ).fieldAlign = <span class="hljs-number">8</span>
|
|
(*rV.typ).kind = <span class="hljs-number">22</span>
|
|
(*(*rV.typ).<span class="hljs-typename">string</span>) = <span class="hljs-string">"*os.File"</span>
|
|
|
|
(*(*(*rV.typ).uncommonType).methods[<span class="hljs-number">0</span>].name) = <span class="hljs-string">"Chdir"</span>
|
|
(*(*(*(*rV.typ).uncommonType).methods[<span class="hljs-number">0</span>].mtyp).<span class="hljs-typename">string</span>) = <span class="hljs-string">"func() error"</span>
|
|
(*(*(*(*rV.typ).uncommonType).methods[<span class="hljs-number">0</span>].typ).<span class="hljs-typename">string</span>) = <span class="hljs-string">"func(*os.File) error"</span>
|
|
...
|
|
</code></pre>
|
|
<p>觀察下面兩個例子的區别：</p>
|
|
<pre><code class="lang-Go"><span class="hljs-keyword">var</span> i <span class="hljs-keyword">interface</span>{} = <span class="hljs-number">3</span>
|
|
|
|
Display(<span class="hljs-string">"i"</span>, i)
|
|
<span class="hljs-comment">// Output:</span>
|
|
<span class="hljs-comment">// Display i (int):</span>
|
|
<span class="hljs-comment">// i = 3</span>
|
|
|
|
Display(<span class="hljs-string">"&i"</span>, &i)
|
|
<span class="hljs-comment">// Output:</span>
|
|
<span class="hljs-comment">// Display &i (*interface {}):</span>
|
|
<span class="hljs-comment">// (*&i).type = int</span>
|
|
<span class="hljs-comment">// (*&i).value = 3</span>
|
|
</code></pre>
|
|
<p>在第一個例子中，Display函數將調用reflect.ValueOf(i)，它返迴一個Int類型的值。正如我們在12.2節中提到的，reflect.ValueOf總是返迴一個值的具體類型，因爲它是從一個接口值提取的內容。</p>
|
|
<p>在第二個例子中，Display函數調用的是reflect.ValueOf(&i)，它返迴一個指向i的指針，對應Ptr類型。在switch的Ptr分支中，通過調用Elem來返迴這個值，返迴一個Value來表示i，對應Interface類型。一個間接獲得的Value，就像這一個，可能代表任意類型的值，包括接口類型。內部的display函數遞歸調用自身，這次它將打印接口的動態類型和值。</p>
|
|
<p>目前的實現，Display如果顯示一個帶環的數據結構將會陷入死循環，例如首位項鏈的鏈表：</p>
|
|
<pre><code class="lang-Go"><span class="hljs-comment">// a struct that points to itself</span>
|
|
<span class="hljs-keyword">type</span> Cycle <span class="hljs-keyword">struct</span>{ Value <span class="hljs-typename">int</span>; Tail *Cycle }
|
|
<span class="hljs-keyword">var</span> c Cycle
|
|
c = Cycle{<span class="hljs-number">42</span>, &c}
|
|
Display(<span class="hljs-string">"c"</span>, c)
|
|
</code></pre>
|
|
<p>Display會永遠不停地進行深度遞歸打印：</p>
|
|
<pre><code class="lang-Go">Display c (display.Cycle):
|
|
c.Value = <span class="hljs-number">42</span>
|
|
(*c.Tail).Value = <span class="hljs-number">42</span>
|
|
(*(*c.Tail).Tail).Value = <span class="hljs-number">42</span>
|
|
(*(*(*c.Tail).Tail).Tail).Value = <span class="hljs-number">42</span>
|
|
...ad infinitum...
|
|
</code></pre>
|
|
<p>許多Go語言程序都包含了一些循環的數據結果。Display支持這類帶環的數據結構是比較棘手的，需要增加一個額外的記録訪問的路徑；代價是昂貴的。一般的解決方案是采用不安全的語言特性，我們將在13.3節看到具體的解決方案。</p>
|
|
<p>帶環的數據結構很少會對fmt.Sprint函數造成問題，因爲它很少嚐試打印完整的數據結構。例如，當它遇到一個指針的時候，它隻是簡單第打印指針的數值。雖然，在打印包含自身的slice或map時可能遇到睏難，但是不保證處理這種是罕見情況卻可以避免額外的麻煩。</p>
|
|
<p><strong>練習 12.1：</strong> 擴展Displayhans，以便它可以顯示包含以結構體或數組作爲map的key類型的值。</p>
|
|
<p><strong>練習 12.2：</strong> 增強display函數的穩健性，通過記録邊界的步數來確保在超出一定限製前放棄遞歸。（在13.3節，我們會看到另一種探測數據結構是否存在環的技術。）</p>
|
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