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2163 lines
83 KiB
HTML
2163 lines
83 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>命令行參數 | Go编程语言</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 2.5.2">
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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="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="../ch1/ch1-03.html" />
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<link rel="prev" href="../ch1/ch1-01.html" />
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</head>
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<body>
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<div class="book" data-level="1.2" data-chapter-title="命令行參數" data-filepath="ch1/ch1-02.md" data-basepath=".." data-revision="Fri Dec 25 2015 12:32:44 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 active" 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 " 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>
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遞歸
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</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">
|
|
|
|
|
|
<a href="../ch9/ch9-02.html">
|
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|
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<i class="fa fa-check"></i>
|
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|
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<b>9.2.</b>
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|
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sync.Mutex互斥鎖
|
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</a>
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|
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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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<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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<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
|
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</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
|
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</a>
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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
|
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</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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<i class="fa fa-check"></i>
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<b>10.3.</b>
|
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|
|
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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|
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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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|
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<i class="fa fa-check"></i>
|
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<b>10.5.</b>
|
|
|
|
匿名導入
|
|
</a>
|
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|
|
|
</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>
|
|
|
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<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>
|
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|
|
</ul>
|
|
</nav>
|
|
</div>
|
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|
|
<div class="book-body">
|
|
<div class="body-inner">
|
|
<div class="book-header" role="navigation">
|
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<!-- Actions Left -->
|
|
|
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|
|
<!-- 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">
|
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<div class="page-inner">
|
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<section class="normal" id="section-">
|
|
|
|
<h2 id="12-命令行參數">1.2. 命令行參數</h2>
|
|
<p>大多數的程序都是處理輸入，産生輸齣；這也正是“計算”的定義。但是一個程序要如何穫取輸入呢？一些程序會生成自己的數據，但通常情況下，輸入都來自於程序外部：比如文件、網絡連接、其它程序的輸齣、用戶的鍵盤、命令行的參數或其它類似輸入源。下面幾個例子會討論其中的一些輸入類型，首先是命令行參數。</p>
|
|
<p>os這個package提供了操作繫統無關（跨平颱）的，與繫統交互的一些函數和相關的變量，運行時程序的命令行參數可以通過os包中一個叫Args的這個變量來穫取；當在os包外部使用該變量時，需要用os.Args來訪問。</p>
|
|
<p>os.Args這個變量是一個字符串（string）的slice（譯註：slice和Python語言中的切片類似，是一個簡版的動態數組），slice在Go語言里是一個基礎的數據結構，之後我們很快會提到。現在可以先把slice當一個簡單的元素序列，可以用類似s[i]的下標訪問形式穫取其內容，併且可以用形如s[m:n]的形式來穫取到一個slice的子集(譯註：和python里的語法差不多)。其長度可以用len(s)函數來穫取。和其它大多數編程語言類似，Go語言里的這種索引形式也采用了左閉右開區間，包括m~n的第一個元素，但不包括最後那個元素（譯註：比如a = [1, 2, 3, 4, 5], a[0:3] = [1, 2, 3]，不包含最後一個元素）。這樣可以簡化我們的處理邏輯。比如s[m:n]這個slice，0 ≤ m ≤ n ≤ len(s)，包含n-m個元素。</p>
|
|
<p>os.Args的第一個元素，卽os.Args[0]是命令行執行時的命令本身；其它的元素則是執行該命令時傳給這個程序的參數。前面提到的切片表達式，s[m:n]會返迴第m到第n-1個元素，所以下一個例子里需要用到的os.Args[1:len(os.Args)]卽是除了命令本身外的所有傳入參數。如果我們省略s[m:n]里的m和n，那麽默認這個表達式會填入0:len(s)，所以這里我們還可以省略掉n，寫成os.Args[1:]。</p>
|
|
<p>下面是一個Unix里echo命令的實現，這個命令會在單行內打印齣命令行參數。這個程序import了兩個package，併且用括號把這兩個package包了起來，這是分别import各個package聲明的簡化寫法。當然了你分開來寫import也沒有什麽問題，隻是一般爲了方便我們都會像下面這樣來導入多個package。我們自己寫的導入順序併不重要，因爲gofmt工具會幫助我們按照字母順序來排列好這些導入包名。（本書中如果一個例子有多種版本時，我們會用編號標記齣來）</p>
|
|
<pre><code class="lang-go">gopl.io/ch1/echo1
|
|
<span class="hljs-comment">// Echo1 prints its command-line arguments.</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-keyword">func</span> main() {
|
|
<span class="hljs-keyword">var</span> s, sep <span class="hljs-typename">string</span>
|
|
<span class="hljs-keyword">for</span> i := <span class="hljs-number">1</span>; i < <span class="hljs-built_in">len</span>(os.Args); i++ {
|
|
s += sep + os.Args[i]
|
|
sep = <span class="hljs-string">" "</span>
|
|
}
|
|
fmt.Println(s)
|
|
}
|
|
</code></pre>
|
|
<p>Go語言里的註釋是以//來表示。//之後的內容一直到行末都是這條註釋的一部分，併且這些註釋會被編譯器忽略。</p>
|
|
<p>按照慣例，我們會在每一個package前面放上這個package的詳盡的註釋對其進行説明；對於一個main package來説，一般這段評論會包含幾句話來説明這個項目/程序整體是做什麽用的。</p>
|
|
<p>var關鍵字用來做變量聲明。這個程序聲明了s和sep兩個string變量。變量可以在聲明期間直接進行初始化。如果沒有顯式地初始化的話，Go語言會隱式地給這些未初始化的變量賦予對應其類型的零值，比如數值類型就是0，字符串類型就是空字符串“”。在這個例子里的s和sep被隱式地賦值爲了空字符串。在第2章中我們會更詳細地講解變量和聲明。</p>
|
|
<p>對於數字類型，Go語言提供了常規的數值計算和邏輯運算符。而對於string類型，+號表示字符串的連接（譯註：和C++或者js是一樣的）。所以下面這個表達式：</p>
|
|
<pre><code class="lang-go">sep + os.Args[i]
|
|
</code></pre>
|
|
<p>表示將sep字符串和os.Args[i]字符串進行連接。我們在程序里用的另外一個表達式：</p>
|
|
<pre><code class="lang-go">s += sep + os.Args[i]
|
|
</code></pre>
|
|
<p>會將sep與os.Args[i]連接，然後再將得到的結果與s進行連接併賦值運給s，這種方式和下面的表達是等價的：</p>
|
|
<pre><code class="lang-go">s = s + sep + os.Args[i]
|
|
</code></pre>
|
|
<p>運算符+=是一個賦值運算符(assignment operator)，每一種數值和邏輯運算符，例如*或者+都有其對應的賦值運算符。</p>
|
|
<p>echo程序可以每循環一次輸齣一個參數，不過我們這里的版本是不斷地將其結果連接到一個字符串的末尾。s這個字符串在聲明的時候是一個空字符串，而之後循環每次都會被在末尾添加一段字符串；第一次迭代之後，一個空格會被插入到字符串末尾，所以每插入一個新值，都會和前一個中間有一個空格隔開。這是一種非線性的操作，當我們的參數數量變得龐大的時候（當然不是説這里的echo，一般echo也不會有太多參數）其運行開銷也會變得龐大。下面我們會介紹一繫列的echo改進版，來應對這里説到的運行效率低下。</p>
|
|
<p>在for循環中，我們用到了i來做下標索引，可以看到我們用了:=符號來給i進行初始化和賦值，這是var xxx=yyy的一種簡寫形式，Go語言會根據等號右邊的值的類型自動判斷左邊的值類型，下一章會對這一點進行詳細説明。</p>
|
|
<p>自增表達式i++會爲i加上1；這和i += 1以及i = i + 1都是等價的。對應的還有i--是給i減去1。這些在Go語言里是語句，而不像C繫的其它語言里是表達式。所以在Go語言里j = i++是非法的，而且++和--都隻能放在變量名後面，因此--i也是非法的。</p>
|
|
<p>在Go語言里隻有for循環一種循環。當然了爲了滿足需求，Go的for循環有很多種形式，下面是其中的一種：</p>
|
|
<pre><code class="lang-go"><span class="hljs-keyword">for</span> initialization; condition; post {
|
|
<span class="hljs-comment">// zero or more statements</span>
|
|
}
|
|
</code></pre>
|
|
<p>這里需要註意，for循環的兩邊是不需要像其它語言一樣寫括號的。併且左大括號需要和for語句在同一行。</p>
|
|
<p>initialization部分是可選的，如果你寫了這部分的話，在for循環之前這部分的邏輯會被執行。需要註意的是這部分必鬚是一個簡單的語句，也就是説是一個簡短的變量聲明，一個賦值語句，或是一個函數調用。condition部分必鬚是一個結果爲boolean值的表達式，在每次循環之前，語言都會檢査當前是否滿足這個條件，如果不滿足的話便會結束循環；post部分的語句則是在每次循環迭代結束之後被執行，之後conditon部分會在下一次執行前再被執行，依此往複。當condition條件里的判斷結果變爲false之後，循環卽結束。</p>
|
|
<p>上面提到是for循環里的三個部分都是可以被省略的，如果你把initialization和post部分都省略的話，那麽連中間隔離他們的分號也是可以被省略的，比如下面這種for循環，就和傳統的while循環是一樣的：</p>
|
|
<pre><code class="lang-go"><span class="hljs-comment">// a traditional "while" loop</span>
|
|
<span class="hljs-keyword">for</span> condition {
|
|
<span class="hljs-comment">// ...</span>
|
|
}
|
|
</code></pre>
|
|
<p>當然了，如果你連唯一的條件都省了，那麽for循環就會變成一個無限循環，像下面這樣：</p>
|
|
<pre><code class="lang-go"><span class="hljs-comment">// a traditional infinite loop</span>
|
|
<span class="hljs-keyword">for</span> {
|
|
<span class="hljs-comment">// ...</span>
|
|
}
|
|
</code></pre>
|
|
<p>在無限循環中，你還是可以靠break或者return語句來終止掉循環。</p>
|
|
<p>如果你的遍歷對象是string或者slice類型值的話，還有另外一種循環的寫法，我們來看看另一個版本的echo：</p>
|
|
<pre><code class="lang-go">gopl.io/ch1/echo2
|
|
<span class="hljs-comment">// Echo2 prints its command-line arguments.</span>
|
|
<span class="hljs-keyword">package</span> main
|
|
|
|
<span class="hljs-keyword">import</span> (
|
|
<span class="hljs-string">"fmt"</span>
|
|
)
|
|
|
|
<span class="hljs-keyword">func</span> main() {
|
|
s, sep := <span class="hljs-string">""</span>, <span class="hljs-string">""</span>
|
|
<span class="hljs-keyword">for</span> _, arg := <span class="hljs-keyword">range</span> os.Args[<span class="hljs-number">1</span>:] {
|
|
s += sep + arg
|
|
sep = <span class="hljs-string">" "</span>
|
|
}
|
|
fmt.Println(s)
|
|
}
|
|
</code></pre>
|
|
<p>每一次循環迭代，range都會返迴一對結果；當前迭代的下標以及在該下標處的元素的值。在這個例子里，我們不需要這個下標，但是因爲range的處理要求我們必鬚要同時處理下標和值。我們可以在這里聲明一個接收index的臨時變量來解決這個問題，但是Go語言又不允許隻聲明而在後續代碼里不使用這個變量，如果你這樣做了編譯器會返迴一個編譯錯誤。</p>
|
|
<p>在Go語言中，應對這種情況的解決方法是用空白標識符，對，就是上面那個下劃線_。空白標識符可以在任何你接收自己不需要處理的值時使用。在這里，我們用它來忽略掉range返迴的那個沒用的下標值。大多數的Go程序員都會像上面這樣來寫類似的os.Args遍歷，由於遍歷os.Args的下標索引是隱式自動生成的，可以避免因顯式更新索引導致的錯誤。</p>
|
|
<p>上面這個版本將s和sep的聲明和初始化都放到了一起，但是我們可以等價地將聲明和賦值分開來寫，下面這些寫法都是等價的</p>
|
|
<pre><code class="lang-go">s := <span class="hljs-string">""</span>
|
|
<span class="hljs-keyword">var</span> s <span class="hljs-typename">string</span>
|
|
<span class="hljs-keyword">var</span> s = <span class="hljs-string">""</span>
|
|
<span class="hljs-keyword">var</span> s <span class="hljs-typename">string</span> = <span class="hljs-string">""</span>
|
|
</code></pre>
|
|
<p>那麽這些等價的形式應該怎麽做選擇呢？這里提供一些建議：第一種形式，隻能用在一個函數內部，而package級别的變量，禁止用這樣的聲明方式。第二種形式依賴於string類型的內部初始化機製，被初始化爲空字符串。第三種形式使用得很少，除非同時聲明多個變量。第四種形式會顯式地標明變量的類型，在多變量同時聲明時可以用到。實踐中你應該隻使用上面的前兩種形式，顯式地指定變量的類型，讓編譯器自己去初始化其值，或者直接用隱式初始化，表明初始值怎麽樣併不重要。</p>
|
|
<p>像上面提到的，每次循環迭代中字符串s都會得到一個新內容。+=語句會分配一個新的字符串，併將老字符串連接起來的值賦予給它。而目標字符串的老字面值在得到新值以後就失去了用處，這些臨時值會被Go語言的垃圾收集器榦掉。</p>
|
|
<p>如果不斷連接的數據量很大，那麽上面這種操作就是成本非常高的操作。更簡單併且有效的一種方式是使用strings包提供的Join函數，像下面這樣：</p>
|
|
<pre><code class="lang-go">gopl.io/ch1/echo3
|
|
<span class="hljs-keyword">func</span> main() {
|
|
fmt.Println(strings.Join(os.Args[<span class="hljs-number">1</span>:], <span class="hljs-string">" "</span>))
|
|
}
|
|
</code></pre>
|
|
<p>最後，如果我們對輸齣的格式也不是很關心，隻是想簡單地輸齣值得的話，還可以像下面這麽寫，Println函數會爲我們自動格式化輸齣。</p>
|
|
<pre><code class="lang-go">fmt.Println(os.Args[<span class="hljs-number">1</span>:])
|
|
</code></pre>
|
|
<p>這個輸齣結果和前面的string.Join得到的結果很相似，隻是被自動地放到了一個方括號里，對slice調用Println函數都會被打印成這樣形式的結果。</p>
|
|
<p><strong>練習 1.1：</strong> 脩改echo程序，使其能夠打印os.Args[0]。</p>
|
|
<p><strong>練習 1.2：</strong> 脩改echo程序，使其打印value和index，每個value和index顯示一行。</p>
|
|
<p><strong>練習 1.3：</strong> 上手實踐前面提到的strings.Join和直接Println，併觀察輸齣結果的區别。</p>
|
|
|
|
|
|
</section>
|
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|
|
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