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2210 lines
80 KiB
HTML
2210 lines
80 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>包和文件 | Go编程语言</title>
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<meta name="apple-mobile-web-app-capable" content="yes">
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<link rel="next" href="../ch2/ch2-07.html" />
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<link rel="prev" href="../ch2/ch2-05.html" />
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</head>
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<body>
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<div class="book" data-level="2.6" data-chapter-title="包和文件" data-filepath="ch2/ch2-06.md" data-basepath=".." data-revision="Thu Dec 24 2015 14:42:02 GMT+0800 (中国标准时间)">
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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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穫取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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併發穫取多個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 active" 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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切片
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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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字典
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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">
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<i class="fa fa-check"></i>
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<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捕穫異常
|
|
</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>
|
|
|
|
併發的退齣
|
|
</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>
|
|
|
|
<li class="chapter " data-level="9.2" data-path="ch9/ch9-02.html">
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<a href="../ch9/ch9-02.html">
|
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<i class="fa fa-check"></i>
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<b>9.2.</b>
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sync.Mutex互斥鎖
|
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</a>
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</li>
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<li class="chapter " data-level="9.3" data-path="ch9/ch9-03.html">
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<a href="../ch9/ch9-03.html">
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<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">
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<a href="../ch9/ch9-04.html">
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<i class="fa fa-check"></i>
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<b>9.4.</b>
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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">
|
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<i class="fa fa-check"></i>
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<b>9.6.</b>
|
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|
競爭條件檢測
|
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</a>
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</li>
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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">
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<i class="fa fa-check"></i>
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<b>9.7.</b>
|
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|
示例: 併發的非阻塞緩存
|
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</a>
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</li>
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<li class="chapter " data-level="9.8" data-path="ch9/ch9-08.html">
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|
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<a href="../ch9/ch9-08.html">
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<i class="fa fa-check"></i>
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<b>9.8.</b>
|
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|
Goroutines和線程
|
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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="10" data-path="ch10/ch10.html">
|
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|
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<a href="../ch10/ch10.html">
|
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<i class="fa fa-check"></i>
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<b>10.</b>
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|
包和工具
|
|
</a>
|
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|
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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>
|
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|
|
簡介
|
|
</a>
|
|
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|
|
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</li>
|
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|
<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>
|
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|
|
導入路徑
|
|
</a>
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|
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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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<i class="fa fa-check"></i>
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<b>10.3.</b>
|
|
|
|
包聲明
|
|
</a>
|
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|
|
</li>
|
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<li class="chapter " data-level="10.4" data-path="ch10/ch10-04.html">
|
|
|
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|
<a href="../ch10/ch10-04.html">
|
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|
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<i class="fa fa-check"></i>
|
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<b>10.4.</b>
|
|
|
|
導入聲明
|
|
</a>
|
|
|
|
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</li>
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<li class="chapter " data-level="10.5" data-path="ch10/ch10-05.html">
|
|
|
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|
<a href="../ch10/ch10-05.html">
|
|
|
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<i class="fa fa-check"></i>
|
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<b>10.5.</b>
|
|
|
|
匿名導入
|
|
</a>
|
|
|
|
|
|
</li>
|
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|
<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 " 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>
|
|
|
|
穫取結構體字段標識
|
|
</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>
|
|
|
|
<div class="book-body">
|
|
<div class="body-inner">
|
|
<div class="book-header" role="navigation">
|
|
<!-- Actions Left -->
|
|
|
|
|
|
<!-- Title -->
|
|
<h1>
|
|
<i class="fa fa-circle-o-notch fa-spin"></i>
|
|
<a href="../" >Go编程语言</a>
|
|
</h1>
|
|
</div>
|
|
|
|
<div class="page-wrapper" tabindex="-1" role="main">
|
|
<div class="page-inner">
|
|
|
|
|
|
<section class="normal" id="section-">
|
|
|
|
<h2 id="26-包和文件">2.6. 包和文件</h2>
|
|
<p>Go語言中的包和其他語言的庫或模塊概念類似, 目的都是爲了支持模塊好, 封裝, 單獨編譯和代碼重用. 一個包的源代碼保存在一個或多個以.爲後綴名的文件中, 通常一個包所在目録路徑的後綴是包的導入路徑; 例如包 gopl.io/ch1/helloworld 對應的目録路徑是 $GOPATH/src/gopl.io/ch1/helloworld.</p>
|
|
<p>每個包作爲一個獨立的名字空間. 例如, 在 image 包中的 Decode 函數 和 unicode/utf16 包中的 Decode 函數是不同的. 要在外部包引用該函數, 必鬚顯式使用 image.Decode 或 utf16.Decode 訪問.</p>
|
|
<p>包可以讓我們通過控製那些名字是外部可見的來隱藏信息. 在Go中, 一個簡單的規則是: 如果一個名字是大寫字母開頭的, 那麽該名字是導齣的.</p>
|
|
<p>爲了演示基本的用法, 假設我們的溫度轉換軟件已經很流行, 我們希望到Go社區也能使用這個包. 我們該如何做呢?</p>
|
|
<p>讓我們創建一個名爲 gopl.io/ch2/tempconv 的包, 是前面例子的一個改進版本. (我們約定我們的例子都是以章節順序來編號的, 這樣的路徑更容易閲讀.) 包代碼存儲在兩個文件, 用來演示如何在一個文件聲明然後在其他的文件訪問; 在現實中, 這樣小的包一般值需要一個文件.</p>
|
|
<p>我們把變量的聲明, 對應的常量, 還有方法都放到 tempconv.go 文件:</p>
|
|
<pre><code class="lang-Go">gopl.io/ch2/tempconv
|
|
<span class="hljs-comment">// Package tempconv performs Celsius and Fahrenheit conversions.</span>
|
|
<span class="hljs-keyword">package</span> tempconv
|
|
|
|
<span class="hljs-keyword">import</span> <span class="hljs-string">"fmt"</span>
|
|
|
|
<span class="hljs-keyword">type</span> Celsius <span class="hljs-typename">float64</span>
|
|
<span class="hljs-keyword">type</span> Fahrenheit <span class="hljs-typename">float64</span>
|
|
|
|
<span class="hljs-keyword">const</span> (
|
|
AbsoluteZeroC Celsius = -<span class="hljs-number">273.15</span>
|
|
FreezingC Celsius = <span class="hljs-number">0</span>
|
|
BoilingC Celsius = <span class="hljs-number">100</span>
|
|
)
|
|
|
|
<span class="hljs-keyword">func</span> (c Celsius) String() <span class="hljs-typename">string</span> { <span class="hljs-keyword">return</span> fmt.Sprintf(<span class="hljs-string">"%g°C"</span>, c) }
|
|
<span class="hljs-keyword">func</span> (f Fahrenheit) String() <span class="hljs-typename">string</span> { <span class="hljs-keyword">return</span> fmt.Sprintf(<span class="hljs-string">"%g°F"</span>, f) }
|
|
</code></pre>
|
|
<p>轉換函數放在 conv.go 文件中:</p>
|
|
<pre><code class="lang-Go"><span class="hljs-keyword">package</span> tempconv
|
|
|
|
<span class="hljs-comment">// CToF converts a Celsius temperature to Fahrenheit.</span>
|
|
<span class="hljs-keyword">func</span> CToF(c Celsius) Fahrenheit { <span class="hljs-keyword">return</span> Fahrenheit(c*<span class="hljs-number">9</span>/<span class="hljs-number">5</span> + <span class="hljs-number">32</span>) }
|
|
|
|
<span class="hljs-comment">// FToC converts a Fahrenheit temperature to Celsius.</span>
|
|
<span class="hljs-keyword">func</span> FToC(f Fahrenheit) Celsius { <span class="hljs-keyword">return</span> Celsius((f - <span class="hljs-number">32</span>) * <span class="hljs-number">5</span> / <span class="hljs-number">9</span>) }
|
|
</code></pre>
|
|
<p>每個文件都是以包的聲明語句開始, 用來指定包的名字. 當包被導入的時候, 包內部的成員將通過類似 tempconv.CToF 的方式訪問. 包級别的名字, 例如在一個文件聲明的類型和常量, 在同一個包的其他文件也是可以直接訪問的,
|
|
就好像所有代碼都在一個文件一樣. 要註意的是 tempconv.go 文件導入了 fmt 包, 但是 conv.go 文件併沒有, 因爲它併沒有用到 fmt 包.</p>
|
|
<p>因爲包級别的常量名都是以大寫字母開頭, 它們也是可以像 tempconv.AbsoluteZeroC 這樣被訪問的:</p>
|
|
<pre><code class="lang-Go">fmt.Printf(<span class="hljs-string">"Brrrr! %v\n"</span>, tempconv.AbsoluteZeroC) <span class="hljs-comment">// "Brrrr! -273.15°C"</span>
|
|
</code></pre>
|
|
<p>要將 攝氏溫度轉換爲 華氏溫度, 需要先導入 gopl.io/ch2/tempconv, 然後就可以使用下面的代碼轉換了:</p>
|
|
<pre><code class="lang-Go">fmt.Println(tempconv.CToF(tempconv.BoilingC)) <span class="hljs-comment">// "212°F"</span>
|
|
</code></pre>
|
|
<p>在每個文件的包聲明前僅跟着的註釋是包註釋(§10.7.4). 通常, 第一句應該先是包的功能概要.
|
|
一個包通常隻有一個文件有包註釋. 如果包註釋很大, 通常會放到一個獨立的 doc.go 文件中.</p>
|
|
<p><strong>練習 2.1:</strong> 向 tempconv 包 添加類型, 常量和函數用來處理 Kelvin 絶對溫度的轉換,
|
|
Kelvin 絶對零度是 −273.15°C, Kelvin 絶對溫度1K和攝氏度1°C的單位間隔是一樣的.</p>
|
|
<h3 id="261-導入包">2.6.1. 導入包</h3>
|
|
<p>在Go程序中, 每個包都是有一個全局唯一的導入路徑. 聲明中類似 "gopl.io/ch2/tempconv" 的字符串對應導入路徑. 語言的規范併沒有定義這些字符串的具體含義或包來自哪里, 它們是由工具來解釋. 當使用 go 工具箱時(第十章), 一個導入路徑代表一個目録中的一個或多個Go源文件.</p>
|
|
<p>除了到導入路徑, 每個包還有一個包名, 包名一般是短小的(也不要求是是唯一的), 包名在包的聲明處指定. 按照慣例, 一個包的名字和包的導入路徑的最後一個字段相同, 例如 gopl.io/ch2/tempconv 包的名字是 tempconv.</p>
|
|
<p>要使用 gopl.io/ch2/tempconv 包, 需要先導入:</p>
|
|
<pre><code class="lang-Go">gopl.io/ch2/cf
|
|
<span class="hljs-comment">// Cf converts its numeric argument to Celsius and Fahrenheit. </span>
|
|
<span class="hljs-keyword">package</span> main
|
|
|
|
<span class="hljs-keyword">import</span> (
|
|
<span class="hljs-string">"fmt"</span>
|
|
<span class="hljs-string">"os"</span>
|
|
<span class="hljs-string">"strconv"</span>
|
|
|
|
<span class="hljs-string">"gopl.io/ch2/tempconv"</span>
|
|
)
|
|
|
|
<span class="hljs-keyword">func</span> main() {
|
|
<span class="hljs-keyword">for</span> _, arg := <span class="hljs-keyword">range</span> os.Args[<span class="hljs-number">1</span>:] {
|
|
t, err := strconv.ParseFloat(arg, <span class="hljs-number">64</span>)
|
|
<span class="hljs-keyword">if</span> err != <span class="hljs-constant">nil</span> {
|
|
fmt.Fprintf(os.Stderr, <span class="hljs-string">"cf: %v\n"</span>, err)
|
|
os.Exit(<span class="hljs-number">1</span>)
|
|
}
|
|
f := tempconv.Fahrenheit(t)
|
|
c := tempconv.Celsius(t)
|
|
fmt.Printf(<span class="hljs-string">"%s = %s, %s = %s\n"</span>,
|
|
f, tempconv.FToC(f), c, tempconv.CToF(c))
|
|
}
|
|
}
|
|
</code></pre>
|
|
<p>導入聲明將導入的包綁定到一個短小的名字, 然後通過該名字就可以引用包中導齣的全部內容. 上面的導入聲明將允許我們以 tempconv.CToF 的方式來訪問 gopl.io/ch2/tempconv 包中的內容. 默認情況下, 導入的包綁定到 tempconv 名字, 但是我們也可以綁定到另一個名稱, 以避免名字衝突(§10.3).</p>
|
|
<p>cf 程序將命令行輸入的一個溫度在 Celsius 和 Fahrenheit 之間轉換:</p>
|
|
<pre><code>$ go build gopl.io/ch2/cf
|
|
$ ./cf 32
|
|
32°F = 0°C, 32°C = 89.6°F
|
|
$ ./cf 212
|
|
212°F = 100°C, 212°C = 413.6°F
|
|
$ ./cf -40
|
|
-40°F = -40°C, -40°C = -40°F
|
|
</code></pre><p>如果導入一個包, 但是沒有使用該包將被當作一個錯誤. 這種強製檢測可以有效減少不必要的依賴, 雖然在調試期間會讓人討厭, 因爲刪除一個類似 log.Print("got here!") 的打印可能導致需要同時刪除 log 包導入聲明, 否則, 編譯器將會發齣一個錯誤. 在這種情況下, 我們需要將不必要的導入刪除或註釋掉.</p>
|
|
<p>不過有更好的解決方案, 我們可以使用 golang.org/x/tools/cmd/goimports 工具, 它可以根據需要自動添加或刪除導入的包; 許多編輯器都可以集成 goimports 工具, 然後在保存文件的時候自動允許它. 類似的還有 gofmt 工具, 可以用來格式化Go源文件.</p>
|
|
<p><strong>練習 2.2:</strong> 寫一個通用的單位轉換程序, 用類似 cf 程序的方式從命令行讀取參數, 如果缺省的話則是從標準輸入讀取參數, 然後做類似 Celsius 和 Fahrenheit 的轉換,
|
|
長度單位對應英尺和米, 重量單位對應磅和公斤 等等.</p>
|
|
<h3 id="262-包的初始化">2.6.2. 包的初始化</h3>
|
|
<p>包的初始化首先是解決包級變量的依賴順序, 然後安裝包級變量聲明齣現的順序依次初始化:</p>
|
|
<pre><code class="lang-Go"><span class="hljs-keyword">var</span> a = b + c <span class="hljs-comment">// a 第三個初始化, 爲 3</span>
|
|
<span class="hljs-keyword">var</span> b = f() <span class="hljs-comment">// b 第二個初始化, 爲 2, 通過調用 f (依賴c)</span>
|
|
<span class="hljs-keyword">var</span> c = <span class="hljs-number">1</span> <span class="hljs-comment">// c 第一個初始化, 爲 1</span>
|
|
|
|
<span class="hljs-keyword">func</span> f() <span class="hljs-typename">int</span> { <span class="hljs-keyword">return</span> c + <span class="hljs-number">1</span> }
|
|
</code></pre>
|
|
<p>如果包中含有多個 .go 文件, 它們按照發給編譯器的順序進行初始化, Go的構建工具首先將 .go 文件根據文件名排序, 然後依次調用編譯器編譯.</p>
|
|
<p>對於在包級别聲明的變量, 如果有初始化表達式則用表達式初始化, 還有一些沒有初始化表達式的, 例如 某些表格數據 初始化併不是一個簡單的賦值過程. 在這種情況下, 我們可以用 init 初始化函數來簡化工作. 每個文件都可以包含多個 init 初始化函數</p>
|
|
<pre><code class="lang-Go"><span class="hljs-keyword">func</span> init() { <span class="hljs-comment">/* ... */</span> }
|
|
</code></pre>
|
|
<p>這樣的init初始化函數除了不能被調用或引用外, 其他行爲和普通函數類似. 在每個文件中的init初始化函數, 在程序開始執行時按照它們聲明的順序被自動調用.</p>
|
|
<p>每個包在解決依賴的前提下, 以導入聲明的順序初始化, 每個包隻會被初始化一次. 因此, 如果一個 p 包導入了 q 包, 那麽在 p 包初始化的時候可以認爲 q 包已經初始化過了. 初始化工作是自下而上進行的, main 包最後被初始化. 以這種方式, 確保 在 main 函數執行之前, 所有的包都已經初始化了.</p>
|
|
<p>下面的代碼定義了一個 PopCount 函數, 用於返迴一個數字中含二進製1bit的個數. 它使用 init 初始化函數來生成輔助表格 pc, pc 表格用於處理每個8bit寬度的數字含二進製的1bit的個數, 這樣的話在處理64bit寬度的數字時就沒有必要循環64次, 隻需要8次査表就可以了. (這併不是最快的統計1bit數目的算法, 但是他可以方便演示init函數的用法, 併且演示了如果預生成輔助表格, 這是編程中常用的技術.)</p>
|
|
<pre><code class="lang-Go">gopl.io/ch2/popcount
|
|
<span class="hljs-keyword">package</span> popcount
|
|
|
|
<span class="hljs-comment">// pc[i] is the population count of i.</span>
|
|
<span class="hljs-keyword">var</span> pc [<span class="hljs-number">256</span>]<span class="hljs-typename">byte</span>
|
|
|
|
<span class="hljs-keyword">func</span> init() {
|
|
<span class="hljs-keyword">for</span> i := <span class="hljs-keyword">range</span> pc {
|
|
pc[i] = pc[i/<span class="hljs-number">2</span>] + <span class="hljs-typename">byte</span>(i&<span class="hljs-number">1</span>)
|
|
}
|
|
}
|
|
|
|
<span class="hljs-comment">// PopCount returns the population count (number of set bits) of x.</span>
|
|
<span class="hljs-keyword">func</span> PopCount(x <span class="hljs-typename">uint64</span>) <span class="hljs-typename">int</span> {
|
|
<span class="hljs-keyword">return</span> <span class="hljs-typename">int</span>(pc[<span class="hljs-typename">byte</span>(x>>(<span class="hljs-number">0</span>*<span class="hljs-number">8</span>))] +
|
|
pc[<span class="hljs-typename">byte</span>(x>>(<span class="hljs-number">1</span>*<span class="hljs-number">8</span>))] +
|
|
pc[<span class="hljs-typename">byte</span>(x>>(<span class="hljs-number">2</span>*<span class="hljs-number">8</span>))] +
|
|
pc[<span class="hljs-typename">byte</span>(x>>(<span class="hljs-number">3</span>*<span class="hljs-number">8</span>))] +
|
|
pc[<span class="hljs-typename">byte</span>(x>>(<span class="hljs-number">4</span>*<span class="hljs-number">8</span>))] +
|
|
pc[<span class="hljs-typename">byte</span>(x>>(<span class="hljs-number">5</span>*<span class="hljs-number">8</span>))] +
|
|
pc[<span class="hljs-typename">byte</span>(x>>(<span class="hljs-number">6</span>*<span class="hljs-number">8</span>))] +
|
|
pc[<span class="hljs-typename">byte</span>(x>>(<span class="hljs-number">7</span>*<span class="hljs-number">8</span>))])
|
|
}
|
|
</code></pre>
|
|
<p>要註意的是 init 函數中, range 循環隻使用了索引, 省略了沒有用到的值部分.
|
|
循環也可以這樣寫:</p>
|
|
<pre><code class="lang-Go"><span class="hljs-keyword">for</span> i, _ := <span class="hljs-keyword">range</span> pc {
|
|
</code></pre>
|
|
<p>我們在下一節和10.5節還將看到其它使用init函數的地方.</p>
|
|
<p><strong>練習2.3:</strong> 重寫 PopCount 函數, 用一個循環代替單一的表達式. 比較兩個版本的性能. (11.4節將展示如何繫統地比較兩個不同實現的性能.)</p>
|
|
<p><strong>練習2.4:</strong> 用移位的算法重寫 PopCount 函數, 每次測試最右邊的1bit, 然後統計總數. 比較和査表算法的性能差異.</p>
|
|
<p><strong>練習2.5:</strong> 表達式 <code>x&(x-1)</code> 用於將 x 的最低的一個1bit位清零. 使用這個格式重寫 PopCount 函數, 然後比較性能.</p>
|
|
|
|
|
|
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