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35 KiB
HTML
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<title>获取结构体字段标签 - Go语言圣经</title>
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<nav id="sidebar" class="sidebar" aria-label="Table of contents">
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<div class="sidebar-scrollbox">
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<ol class="chapter">
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<li class="chapter-item expanded ">
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<a href="../index.html" >Go语言圣经</a>
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<li class="chapter-item expanded ">
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<a href="../preface-zh.html" >译者序</a>
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<li class="chapter-item expanded ">
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<a href="../preface.html" >前言</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch1/ch1.html" ><strong aria-hidden="true">1.</strong> 入门</a>
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</li>
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<ol class="section">
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<li class="chapter-item expanded ">
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<a href="../ch1/ch1-01.html" ><strong aria-hidden="true">1.1.</strong> Hello, World</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch1/ch1-02.html" ><strong aria-hidden="true">1.2.</strong> 命令行参数</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch1/ch1-03.html" ><strong aria-hidden="true">1.3.</strong> 查找重复的行</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch1/ch1-04.html" ><strong aria-hidden="true">1.4.</strong> GIF动画</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch1/ch1-05.html" ><strong aria-hidden="true">1.5.</strong> 获取URL</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch1/ch1-06.html" ><strong aria-hidden="true">1.6.</strong> 并发获取多个URL</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch1/ch1-07.html" ><strong aria-hidden="true">1.7.</strong> Web服务</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch1/ch1-08.html" ><strong aria-hidden="true">1.8.</strong> 本章要点</a>
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</li>
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</ol>
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<li class="chapter-item expanded ">
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<a href="../ch2/ch2.html" ><strong aria-hidden="true">2.</strong> 程序结构</a>
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</li>
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<ol class="section">
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<li class="chapter-item expanded ">
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<a href="../ch2/ch2-01.html" ><strong aria-hidden="true">2.1.</strong> 命名</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch2/ch2-02.html" ><strong aria-hidden="true">2.2.</strong> 声明</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch2/ch2-03.html" ><strong aria-hidden="true">2.3.</strong> 变量</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch2/ch2-04.html" ><strong aria-hidden="true">2.4.</strong> 赋值</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch2/ch2-05.html" ><strong aria-hidden="true">2.5.</strong> 类型</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch2/ch2-06.html" ><strong aria-hidden="true">2.6.</strong> 包和文件</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch2/ch2-07.html" ><strong aria-hidden="true">2.7.</strong> 作用域</a>
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</li>
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</ol>
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<li class="chapter-item expanded ">
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<a href="../ch3/ch3.html" ><strong aria-hidden="true">3.</strong> 基础数据类型</a>
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</li>
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<ol class="section">
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<li class="chapter-item expanded ">
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<a href="../ch3/ch3-01.html" ><strong aria-hidden="true">3.1.</strong> 整型</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch3/ch3-02.html" ><strong aria-hidden="true">3.2.</strong> 浮点数</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch3/ch3-03.html" ><strong aria-hidden="true">3.3.</strong> 复数</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch3/ch3-04.html" ><strong aria-hidden="true">3.4.</strong> 布尔型</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch3/ch3-05.html" ><strong aria-hidden="true">3.5.</strong> 字符串</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch3/ch3-06.html" ><strong aria-hidden="true">3.6.</strong> 常量</a>
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</li>
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</ol>
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<li class="chapter-item expanded ">
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<a href="../ch4/ch4.html" ><strong aria-hidden="true">4.</strong> 复合数据类型</a>
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</li>
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<ol class="section">
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<li class="chapter-item expanded ">
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<a href="../ch4/ch4-01.html" ><strong aria-hidden="true">4.1.</strong> 数组</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch4/ch4-02.html" ><strong aria-hidden="true">4.2.</strong> Slice</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch4/ch4-03.html" ><strong aria-hidden="true">4.3.</strong> Map</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch4/ch4-04.html" ><strong aria-hidden="true">4.4.</strong> 结构体</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch4/ch4-05.html" ><strong aria-hidden="true">4.5.</strong> JSON</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch4/ch4-06.html" ><strong aria-hidden="true">4.6.</strong> 文本和HTML模板</a>
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</li>
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</ol>
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<li class="chapter-item expanded ">
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<a href="../ch5/ch5.html" ><strong aria-hidden="true">5.</strong> 函数</a>
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</li>
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<ol class="section">
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<li class="chapter-item expanded ">
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<a href="../ch5/ch5-01.html" ><strong aria-hidden="true">5.1.</strong> 函数声明</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch5/ch5-02.html" ><strong aria-hidden="true">5.2.</strong> 递归</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch5/ch5-03.html" ><strong aria-hidden="true">5.3.</strong> 多返回值</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch5/ch5-04.html" ><strong aria-hidden="true">5.4.</strong> 错误</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch5/ch5-05.html" ><strong aria-hidden="true">5.5.</strong> 函数值</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch5/ch5-06.html" ><strong aria-hidden="true">5.6.</strong> 匿名函数</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch5/ch5-07.html" ><strong aria-hidden="true">5.7.</strong> 可变参数</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch5/ch5-08.html" ><strong aria-hidden="true">5.8.</strong> Deferred函数</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch5/ch5-09.html" ><strong aria-hidden="true">5.9.</strong> Panic异常</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch5/ch5-10.html" ><strong aria-hidden="true">5.10.</strong> Recover捕获异常</a>
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</li>
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</ol>
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<li class="chapter-item expanded ">
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<a href="../ch6/ch6.html" ><strong aria-hidden="true">6.</strong> 方法</a>
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</li>
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<ol class="section">
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<li class="chapter-item expanded ">
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<a href="../ch6/ch6-01.html" ><strong aria-hidden="true">6.1.</strong> 方法声明</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch6/ch6-02.html" ><strong aria-hidden="true">6.2.</strong> 基于指针对象的方法</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch6/ch6-03.html" ><strong aria-hidden="true">6.3.</strong> 通过嵌入结构体来扩展类型</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch6/ch6-04.html" ><strong aria-hidden="true">6.4.</strong> 方法值和方法表达式</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch6/ch6-05.html" ><strong aria-hidden="true">6.5.</strong> 示例: Bit数组</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch6/ch6-06.html" ><strong aria-hidden="true">6.6.</strong> 封装</a>
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</li>
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</ol>
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<li class="chapter-item expanded ">
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<a href="../ch7/ch7.html" ><strong aria-hidden="true">7.</strong> 接口</a>
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</li>
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<ol class="section">
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<li class="chapter-item expanded ">
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<a href="../ch7/ch7-01.html" ><strong aria-hidden="true">7.1.</strong> 接口是合约</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch7/ch7-02.html" ><strong aria-hidden="true">7.2.</strong> 接口类型</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch7/ch7-03.html" ><strong aria-hidden="true">7.3.</strong> 实现接口的条件</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch7/ch7-04.html" ><strong aria-hidden="true">7.4.</strong> flag.Value接口</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch7/ch7-05.html" ><strong aria-hidden="true">7.5.</strong> 接口值</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch7/ch7-06.html" ><strong aria-hidden="true">7.6.</strong> sort.Interface接口</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch7/ch7-07.html" ><strong aria-hidden="true">7.7.</strong> http.Handler接口</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch7/ch7-08.html" ><strong aria-hidden="true">7.8.</strong> error接口</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch7/ch7-09.html" ><strong aria-hidden="true">7.9.</strong> 示例: 表达式求值</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch7/ch7-10.html" ><strong aria-hidden="true">7.10.</strong> 类型断言</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch7/ch7-11.html" ><strong aria-hidden="true">7.11.</strong> 基于类型断言识别错误类型</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch7/ch7-12.html" ><strong aria-hidden="true">7.12.</strong> 通过类型断言查询接口</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch7/ch7-13.html" ><strong aria-hidden="true">7.13.</strong> 类型分支</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch7/ch7-14.html" ><strong aria-hidden="true">7.14.</strong> 示例: 基于标记的XML解码</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch7/ch7-15.html" ><strong aria-hidden="true">7.15.</strong> 补充几点</a>
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</li>
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</ol>
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<li class="chapter-item expanded ">
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<a href="../ch8/ch8.html" ><strong aria-hidden="true">8.</strong> Goroutines和Channels</a>
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</li>
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<ol class="section">
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<li class="chapter-item expanded ">
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<a href="../ch8/ch8-01.html" ><strong aria-hidden="true">8.1.</strong> Goroutines</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch8/ch8-02.html" ><strong aria-hidden="true">8.2.</strong> 示例: 并发的Clock服务</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch8/ch8-03.html" ><strong aria-hidden="true">8.3.</strong> 示例: 并发的Echo服务</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch8/ch8-04.html" ><strong aria-hidden="true">8.4.</strong> Channels</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch8/ch8-05.html" ><strong aria-hidden="true">8.5.</strong> 并发的循环</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch8/ch8-06.html" ><strong aria-hidden="true">8.6.</strong> 示例: 并发的Web爬虫</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch8/ch8-07.html" ><strong aria-hidden="true">8.7.</strong> 基于select的多路复用</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch8/ch8-08.html" ><strong aria-hidden="true">8.8.</strong> 示例: 并发的目录遍历</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch8/ch8-09.html" ><strong aria-hidden="true">8.9.</strong> 并发的退出</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch8/ch8-10.html" ><strong aria-hidden="true">8.10.</strong> 示例: 聊天服务</a>
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</li>
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</ol>
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<li class="chapter-item expanded ">
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<a href="../ch9/ch9.html" ><strong aria-hidden="true">9.</strong> 基于共享变量的并发</a>
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</li>
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<ol class="section">
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<li class="chapter-item expanded ">
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<a href="../ch9/ch9-01.html" ><strong aria-hidden="true">9.1.</strong> 竞争条件</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch9/ch9-02.html" ><strong aria-hidden="true">9.2.</strong> sync.Mutex互斥锁</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch9/ch9-03.html" ><strong aria-hidden="true">9.3.</strong> sync.RWMutex读写锁</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch9/ch9-04.html" ><strong aria-hidden="true">9.4.</strong> 内存同步</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch9/ch9-05.html" ><strong aria-hidden="true">9.5.</strong> sync.Once惰性初始化</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch9/ch9-06.html" ><strong aria-hidden="true">9.6.</strong> 竞争条件检测</a>
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</li>
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<li class="chapter-item expanded ">
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<a href="../ch9/ch9-07.html" ><strong aria-hidden="true">9.7.</strong> 示例: 并发的非阻塞缓存</a>
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</li>
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<li class="chapter-item expanded ">
|
||
<a href="../ch9/ch9-08.html" ><strong aria-hidden="true">9.8.</strong> Goroutines和线程</a>
|
||
</li>
|
||
</ol>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch10/ch10.html" ><strong aria-hidden="true">10.</strong> 包和工具</a>
|
||
</li>
|
||
<ol class="section">
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch10/ch10-01.html" ><strong aria-hidden="true">10.1.</strong> 包简介</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch10/ch10-02.html" ><strong aria-hidden="true">10.2.</strong> 导入路径</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch10/ch10-03.html" ><strong aria-hidden="true">10.3.</strong> 包声明</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch10/ch10-04.html" ><strong aria-hidden="true">10.4.</strong> 导入声明</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch10/ch10-05.html" ><strong aria-hidden="true">10.5.</strong> 包的匿名导入</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch10/ch10-06.html" ><strong aria-hidden="true">10.6.</strong> 包和命名</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch10/ch10-07.html" ><strong aria-hidden="true">10.7.</strong> 工具</a>
|
||
</li>
|
||
</ol>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch11/ch11.html" ><strong aria-hidden="true">11.</strong> 测试</a>
|
||
</li>
|
||
<ol class="section">
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch11/ch11-01.html" ><strong aria-hidden="true">11.1.</strong> go test</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch11/ch11-02.html" ><strong aria-hidden="true">11.2.</strong> 测试函数</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch11/ch11-03.html" ><strong aria-hidden="true">11.3.</strong> 测试覆盖率</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch11/ch11-04.html" ><strong aria-hidden="true">11.4.</strong> 基准测试</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch11/ch11-05.html" ><strong aria-hidden="true">11.5.</strong> 剖析</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch11/ch11-06.html" ><strong aria-hidden="true">11.6.</strong> 示例函数</a>
|
||
</li>
|
||
</ol>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch12/ch12.html" ><strong aria-hidden="true">12.</strong> 反射</a>
|
||
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|
||
<ol class="section">
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch12/ch12-01.html" ><strong aria-hidden="true">12.1.</strong> 为何需要反射?</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch12/ch12-02.html" ><strong aria-hidden="true">12.2.</strong> reflect.Type和reflect.Value</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch12/ch12-03.html" ><strong aria-hidden="true">12.3.</strong> Display递归打印</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch12/ch12-04.html" ><strong aria-hidden="true">12.4.</strong> 示例: 编码S表达式</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch12/ch12-05.html" ><strong aria-hidden="true">12.5.</strong> 通过reflect.Value修改值</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch12/ch12-06.html" ><strong aria-hidden="true">12.6.</strong> 示例: 解码S表达式</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch12/ch12-07.html" class="active"><strong aria-hidden="true">12.7.</strong> 获取结构体字段标签</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch12/ch12-08.html" ><strong aria-hidden="true">12.8.</strong> 显示一个类型的方法集</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch12/ch12-09.html" ><strong aria-hidden="true">12.9.</strong> 几点忠告</a>
|
||
</li>
|
||
</ol>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch13/ch13.html" ><strong aria-hidden="true">13.</strong> 底层编程</a>
|
||
</li>
|
||
<ol class="section">
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch13/ch13-01.html" ><strong aria-hidden="true">13.1.</strong> unsafe.Sizeof, Alignof 和 Offsetof</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch13/ch13-02.html" ><strong aria-hidden="true">13.2.</strong> unsafe.Pointer</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch13/ch13-03.html" ><strong aria-hidden="true">13.3.</strong> 示例: 深度相等判断</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch13/ch13-04.html" ><strong aria-hidden="true">13.4.</strong> 通过cgo调用C代码</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch13/ch13-05.html" ><strong aria-hidden="true">13.5.</strong> 几点忠告</a>
|
||
</li>
|
||
</ol>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../appendix/appendix.html" ><strong aria-hidden="true">14.</strong> 附录</a>
|
||
</li>
|
||
<ol class="section">
|
||
<li class="chapter-item expanded ">
|
||
<a href="../appendix/appendix-a-errata.html" ><strong aria-hidden="true">14.1.</strong> 附录A：原文勘误</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../appendix/appendix-b-author.html" ><strong aria-hidden="true">14.2.</strong> 附录B：作者译者</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../appendix/appendix-c-cpoyright.html" ><strong aria-hidden="true">14.3.</strong> 附录C：译文授权</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../appendix/appendix-d-translations.html" ><strong aria-hidden="true">14.4.</strong> 附录D：其它语言</a>
|
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|
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<main>
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<ul dir="auto"><li><em>凹语言(Go实现, 面向WASM设计): <a href="https://github.com/wa-lang/wa">https://github.com/wa-lang/wa</a></em></li><li><em>WaBook(Go语言实现的MD电子书构建工具): <a href="https://github.com/wa-lang/wabook">https://github.com/wa-lang/wabook</a></em></li></ul><hr>
|
||
|
||
<h2>12.7. 获取结构体字段标签</h2>
|
||
<p>在4.5节我们使用构体成员标签用于设置对应JSON对应的名字。其中json成员标签让我们可以选择成员的名字和抑制零值成员的输出。在本节，我们将看到如何通过反射机制类获取成员标签。</p>
|
||
<p>对于一个web服务，大部分HTTP处理函数要做的第一件事情就是展开请求中的参数到本地变量中。我们定义了一个工具函数，叫params.Unpack，通过使用结构体成员标签机制来让HTTP处理函数解析请求参数更方便。</p>
|
||
<p>首先，我们看看如何使用它。下面的search函数是一个HTTP请求处理函数。它定义了一个匿名结构体类型的变量，用结构体的每个成员表示HTTP请求的参数。其中结构体成员标签指明了对于请求参数的名字，为了减少URL的长度这些参数名通常都是神秘的缩略词。Unpack将请求参数填充到合适的结构体成员中，这样我们可以方便地通过合适的类型类来访问这些参数。</p>
|
||
<p><!-- raw HTML omitted --><!-- raw HTML omitted -->gopl.io/ch12/search<!-- raw HTML omitted --><!-- raw HTML omitted --></p>
|
||
<pre><code class="language-Go">import "gopl.io/ch12/params"
|
||
|
||
// search implements the /search URL endpoint.
|
||
func search(resp http.ResponseWriter, req *http.Request) {
|
||
var data struct {
|
||
Labels []string `http:"l"`
|
||
MaxResults int `http:"max"`
|
||
Exact bool `http:"x"`
|
||
}
|
||
data.MaxResults = 10 // set default
|
||
if err := params.Unpack(req, &data); err != nil {
|
||
http.Error(resp, err.Error(), http.StatusBadRequest) // 400
|
||
return
|
||
}
|
||
|
||
// ...rest of handler...
|
||
fmt.Fprintf(resp, "Search: %+v\n", data)
|
||
}
|
||
</code></pre>
|
||
<p>下面的Unpack函数主要完成三件事情。第一，它调用req.ParseForm()来解析HTTP请求。然后，req.Form将包含所有的请求参数，不管HTTP客户端使用的是GET还是POST请求方法。</p>
|
||
<p>下一步，Unpack函数将构建每个结构体成员有效参数名字到成员变量的映射。如果结构体成员有成员标签的话，有效参数名字可能和实际的成员名字不相同。reflect.Type的Field方法将返回一个reflect.StructField，里面含有每个成员的名字、类型和可选的成员标签等信息。其中成员标签信息对应reflect.StructTag类型的字符串，并且提供了Get方法用于解析和根据特定key提取的子串，例如这里的http:"..."形式的子串。</p>
|
||
<p><!-- raw HTML omitted --><!-- raw HTML omitted -->gopl.io/ch12/params<!-- raw HTML omitted --><!-- raw HTML omitted --></p>
|
||
<pre><code class="language-Go">// Unpack populates the fields of the struct pointed to by ptr
|
||
// from the HTTP request parameters in req.
|
||
func Unpack(req *http.Request, ptr interface{}) error {
|
||
if err := req.ParseForm(); err != nil {
|
||
return err
|
||
}
|
||
|
||
// Build map of fields keyed by effective name.
|
||
fields := make(map[string]reflect.Value)
|
||
v := reflect.ValueOf(ptr).Elem() // the struct variable
|
||
for i := 0; i < v.NumField(); i++ {
|
||
fieldInfo := v.Type().Field(i) // a reflect.StructField
|
||
tag := fieldInfo.Tag // a reflect.StructTag
|
||
name := tag.Get("http")
|
||
if name == "" {
|
||
name = strings.ToLower(fieldInfo.Name)
|
||
}
|
||
fields[name] = v.Field(i)
|
||
}
|
||
|
||
// Update struct field for each parameter in the request.
|
||
for name, values := range req.Form {
|
||
f := fields[name]
|
||
if !f.IsValid() {
|
||
continue // ignore unrecognized HTTP parameters
|
||
}
|
||
for _, value := range values {
|
||
if f.Kind() == reflect.Slice {
|
||
elem := reflect.New(f.Type().Elem()).Elem()
|
||
if err := populate(elem, value); err != nil {
|
||
return fmt.Errorf("%s: %v", name, err)
|
||
}
|
||
f.Set(reflect.Append(f, elem))
|
||
} else {
|
||
if err := populate(f, value); err != nil {
|
||
return fmt.Errorf("%s: %v", name, err)
|
||
}
|
||
}
|
||
}
|
||
}
|
||
return nil
|
||
}
|
||
</code></pre>
|
||
<p>最后，Unpack遍历HTTP请求的name/valu参数键值对，并且根据更新相应的结构体成员。回想一下，同一个名字的参数可能出现多次。如果发生这种情况，并且对应的结构体成员是一个slice，那么就将所有的参数添加到slice中。其它情况，对应的成员值将被覆盖，只有最后一次出现的参数值才是起作用的。</p>
|
||
<p>populate函数小心用请求的字符串类型参数值来填充单一的成员v（或者是slice类型成员中的单一的元素）。目前，它仅支持字符串、有符号整数和布尔型。其中其它的类型将留做练习任务。</p>
|
||
<pre><code class="language-Go">func populate(v reflect.Value, value string) error {
|
||
switch v.Kind() {
|
||
case reflect.String:
|
||
v.SetString(value)
|
||
|
||
case reflect.Int:
|
||
i, err := strconv.ParseInt(value, 10, 64)
|
||
if err != nil {
|
||
return err
|
||
}
|
||
v.SetInt(i)
|
||
|
||
case reflect.Bool:
|
||
b, err := strconv.ParseBool(value)
|
||
if err != nil {
|
||
return err
|
||
}
|
||
v.SetBool(b)
|
||
|
||
default:
|
||
return fmt.Errorf("unsupported kind %s", v.Type())
|
||
}
|
||
return nil
|
||
}
|
||
</code></pre>
|
||
<p>如果我们上上面的处理程序添加到一个web服务器，则可以产生以下的会话：</p>
|
||
<pre><code>$ go build gopl.io/ch12/search
|
||
$ ./search &
|
||
$ ./fetch 'http://localhost:12345/search'
|
||
Search: {Labels:[] MaxResults:10 Exact:false}
|
||
$ ./fetch 'http://localhost:12345/search?l=golang&l=programming'
|
||
Search: {Labels:[golang programming] MaxResults:10 Exact:false}
|
||
$ ./fetch 'http://localhost:12345/search?l=golang&l=programming&max=100'
|
||
Search: {Labels:[golang programming] MaxResults:100 Exact:false}
|
||
$ ./fetch 'http://localhost:12345/search?x=true&l=golang&l=programming'
|
||
Search: {Labels:[golang programming] MaxResults:10 Exact:true}
|
||
$ ./fetch 'http://localhost:12345/search?q=hello&x=123'
|
||
x: strconv.ParseBool: parsing "123": invalid syntax
|
||
$ ./fetch 'http://localhost:12345/search?q=hello&max=lots'
|
||
max: strconv.ParseInt: parsing "lots": invalid syntax
|
||
</code></pre>
|
||
<p><strong>练习 12.11：</strong> 编写相应的Pack函数，给定一个结构体值，Pack函数将返回合并了所有结构体成员和值的URL。</p>
|
||
<p><strong>练习 12.12：</strong> 扩展成员标签以表示一个请求参数的有效值规则。例如，一个字符串可以是有效的email地址或一个信用卡号码，还有一个整数可能需要是有效的邮政编码。修改Unpack函数以检查这些规则。</p>
|
||
<p><strong>练习 12.13：</strong> 修改S表达式的编码器（§12.4）和解码器（§12.6），采用和encoding/json包（§4.5）类似的方式使用成员标签中的sexpr:"..."字串。</p>
|
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|
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