mirror of
https://github.com/gopl-zh/gopl-zh.github.com.git
synced 2024-11-28 00:58:54 +00:00
667 lines
34 KiB
HTML
667 lines
34 KiB
HTML
<!DOCTYPE HTML>
|
||
<html lang="zh" class="sidebar-visible no-js light">
|
||
<head>
|
||
<!-- Book generated using https://github.com/wa-lang/wabook -->
|
||
<meta charset="UTF-8">
|
||
<title>通过reflect.Value修改值 - Go语言圣经</title>
|
||
<!-- Custom HTML head -->
|
||
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
|
||
<meta name="description" content="">
|
||
<meta name="viewport" content="width=device-width, initial-scale=1">
|
||
<meta name="theme-color" content="#ffffff" />
|
||
|
||
<link rel="icon" href="../favicon.svg">
|
||
<link rel="shortcut icon" href="../favicon.png">
|
||
<link rel="stylesheet" href="../static/wabook/css/variables.css">
|
||
<link rel="stylesheet" href="../static/wabook/css/general.css">
|
||
<link rel="stylesheet" href="../static/wabook/css/chrome.css">
|
||
<link rel="stylesheet" href="../static/wabook/css/print.css" media="print">
|
||
<!-- Fonts -->
|
||
<link rel="stylesheet" href="../static/wabook/FontAwesome/css/font-awesome.css">
|
||
<link rel="stylesheet" href="../static/wabook/fonts/fonts.css">
|
||
<!-- Highlight.js Stylesheets -->
|
||
<link rel="stylesheet" href="../static/wabook/highlight.css">
|
||
<link rel="stylesheet" href="../static/wabook/tomorrow-night.css">
|
||
<link rel="stylesheet" href="../static/wabook/ayu-highlight.css">
|
||
|
||
<!-- Custom theme stylesheets -->
|
||
</head>
|
||
<body>
|
||
<!-- Provide site root to javascript -->
|
||
<script type="text/javascript">
|
||
var path_to_root = "../";
|
||
var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "navy" : "light";
|
||
</script>
|
||
|
||
<!-- Work around some values being stored in localStorage wrapped in quotes -->
|
||
<script type="text/javascript">
|
||
try {
|
||
var theme = localStorage.getItem('wabook-theme');
|
||
var sidebar = localStorage.getItem('wabook-sidebar');
|
||
|
||
if (theme.startsWith('"') && theme.endsWith('"')) {
|
||
localStorage.setItem('wabook-theme', theme.slice(1, theme.length - 1));
|
||
}
|
||
|
||
if (sidebar.startsWith('"') && sidebar.endsWith('"')) {
|
||
localStorage.setItem('wabook-sidebar', sidebar.slice(1, sidebar.length - 1));
|
||
}
|
||
} catch (e) { }
|
||
</script>
|
||
|
||
<!-- Set the theme before any content is loaded, prevents flash -->
|
||
<script type="text/javascript">
|
||
var theme;
|
||
try { theme = localStorage.getItem('wabook-theme'); } catch(e) { }
|
||
if (theme === null || theme === undefined) { theme = default_theme; }
|
||
var html = document.querySelector('html');
|
||
html.classList.remove('no-js')
|
||
html.classList.remove('light')
|
||
html.classList.add(theme);
|
||
html.classList.add('js');
|
||
</script>
|
||
|
||
<!-- Hide / unhide sidebar before it is displayed -->
|
||
<script type="text/javascript">
|
||
var html = document.querySelector('html');
|
||
var sidebar = 'hidden';
|
||
if (document.body.clientWidth >= 1080) {
|
||
try { sidebar = localStorage.getItem('wabook-sidebar'); } catch(e) { }
|
||
sidebar = sidebar || 'visible';
|
||
}
|
||
html.classList.remove('sidebar-visible');
|
||
html.classList.add("sidebar-" + sidebar);
|
||
</script>
|
||
|
||
<nav id="sidebar" class="sidebar" aria-label="Table of contents">
|
||
<div class="sidebar-scrollbox">
|
||
<ol class="chapter">
|
||
<li class="chapter-item expanded ">
|
||
<a href="../index.html" >Go语言圣经</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../preface-zh.html" >译者序</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../preface.html" >前言</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch1/ch1.html" ><strong aria-hidden="true">1.</strong> 入门</a>
|
||
</li>
|
||
<ol class="section">
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch1/ch1-01.html" ><strong aria-hidden="true">1.1.</strong> Hello, World</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch1/ch1-02.html" ><strong aria-hidden="true">1.2.</strong> 命令行参数</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch1/ch1-03.html" ><strong aria-hidden="true">1.3.</strong> 查找重复的行</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch1/ch1-04.html" ><strong aria-hidden="true">1.4.</strong> GIF动画</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch1/ch1-05.html" ><strong aria-hidden="true">1.5.</strong> 获取URL</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch1/ch1-06.html" ><strong aria-hidden="true">1.6.</strong> 并发获取多个URL</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch1/ch1-07.html" ><strong aria-hidden="true">1.7.</strong> Web服务</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch1/ch1-08.html" ><strong aria-hidden="true">1.8.</strong> 本章要点</a>
|
||
</li>
|
||
</ol>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch2/ch2.html" ><strong aria-hidden="true">2.</strong> 程序结构</a>
|
||
</li>
|
||
<ol class="section">
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch2/ch2-01.html" ><strong aria-hidden="true">2.1.</strong> 命名</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch2/ch2-02.html" ><strong aria-hidden="true">2.2.</strong> 声明</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch2/ch2-03.html" ><strong aria-hidden="true">2.3.</strong> 变量</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch2/ch2-04.html" ><strong aria-hidden="true">2.4.</strong> 赋值</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch2/ch2-05.html" ><strong aria-hidden="true">2.5.</strong> 类型</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch2/ch2-06.html" ><strong aria-hidden="true">2.6.</strong> 包和文件</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch2/ch2-07.html" ><strong aria-hidden="true">2.7.</strong> 作用域</a>
|
||
</li>
|
||
</ol>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch3/ch3.html" ><strong aria-hidden="true">3.</strong> 基础数据类型</a>
|
||
</li>
|
||
<ol class="section">
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch3/ch3-01.html" ><strong aria-hidden="true">3.1.</strong> 整型</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch3/ch3-02.html" ><strong aria-hidden="true">3.2.</strong> 浮点数</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch3/ch3-03.html" ><strong aria-hidden="true">3.3.</strong> 复数</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch3/ch3-04.html" ><strong aria-hidden="true">3.4.</strong> 布尔型</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch3/ch3-05.html" ><strong aria-hidden="true">3.5.</strong> 字符串</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch3/ch3-06.html" ><strong aria-hidden="true">3.6.</strong> 常量</a>
|
||
</li>
|
||
</ol>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch4/ch4.html" ><strong aria-hidden="true">4.</strong> 复合数据类型</a>
|
||
</li>
|
||
<ol class="section">
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch4/ch4-01.html" ><strong aria-hidden="true">4.1.</strong> 数组</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch4/ch4-02.html" ><strong aria-hidden="true">4.2.</strong> Slice</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch4/ch4-03.html" ><strong aria-hidden="true">4.3.</strong> Map</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch4/ch4-04.html" ><strong aria-hidden="true">4.4.</strong> 结构体</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch4/ch4-05.html" ><strong aria-hidden="true">4.5.</strong> JSON</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch4/ch4-06.html" ><strong aria-hidden="true">4.6.</strong> 文本和HTML模板</a>
|
||
</li>
|
||
</ol>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch5/ch5.html" ><strong aria-hidden="true">5.</strong> 函数</a>
|
||
</li>
|
||
<ol class="section">
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch5/ch5-01.html" ><strong aria-hidden="true">5.1.</strong> 函数声明</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch5/ch5-02.html" ><strong aria-hidden="true">5.2.</strong> 递归</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch5/ch5-03.html" ><strong aria-hidden="true">5.3.</strong> 多返回值</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch5/ch5-04.html" ><strong aria-hidden="true">5.4.</strong> 错误</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch5/ch5-05.html" ><strong aria-hidden="true">5.5.</strong> 函数值</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch5/ch5-06.html" ><strong aria-hidden="true">5.6.</strong> 匿名函数</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch5/ch5-07.html" ><strong aria-hidden="true">5.7.</strong> 可变参数</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch5/ch5-08.html" ><strong aria-hidden="true">5.8.</strong> Deferred函数</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch5/ch5-09.html" ><strong aria-hidden="true">5.9.</strong> Panic异常</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch5/ch5-10.html" ><strong aria-hidden="true">5.10.</strong> Recover捕获异常</a>
|
||
</li>
|
||
</ol>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch6/ch6.html" ><strong aria-hidden="true">6.</strong> 方法</a>
|
||
</li>
|
||
<ol class="section">
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch6/ch6-01.html" ><strong aria-hidden="true">6.1.</strong> 方法声明</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch6/ch6-02.html" ><strong aria-hidden="true">6.2.</strong> 基于指针对象的方法</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<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>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch6/ch6-04.html" ><strong aria-hidden="true">6.4.</strong> 方法值和方法表达式</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch6/ch6-05.html" ><strong aria-hidden="true">6.5.</strong> 示例: Bit数组</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch6/ch6-06.html" ><strong aria-hidden="true">6.6.</strong> 封装</a>
|
||
</li>
|
||
</ol>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch7/ch7.html" ><strong aria-hidden="true">7.</strong> 接口</a>
|
||
</li>
|
||
<ol class="section">
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch7/ch7-01.html" ><strong aria-hidden="true">7.1.</strong> 接口是合约</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch7/ch7-02.html" ><strong aria-hidden="true">7.2.</strong> 接口类型</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch7/ch7-03.html" ><strong aria-hidden="true">7.3.</strong> 实现接口的条件</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch7/ch7-04.html" ><strong aria-hidden="true">7.4.</strong> flag.Value接口</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch7/ch7-05.html" ><strong aria-hidden="true">7.5.</strong> 接口值</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch7/ch7-06.html" ><strong aria-hidden="true">7.6.</strong> sort.Interface接口</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch7/ch7-07.html" ><strong aria-hidden="true">7.7.</strong> http.Handler接口</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch7/ch7-08.html" ><strong aria-hidden="true">7.8.</strong> error接口</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch7/ch7-09.html" ><strong aria-hidden="true">7.9.</strong> 示例: 表达式求值</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch7/ch7-10.html" ><strong aria-hidden="true">7.10.</strong> 类型断言</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<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>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch7/ch7-12.html" ><strong aria-hidden="true">7.12.</strong> 通过类型断言查询接口</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch7/ch7-13.html" ><strong aria-hidden="true">7.13.</strong> 类型分支</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch7/ch7-14.html" ><strong aria-hidden="true">7.14.</strong> 示例: 基于标记的XML解码</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch7/ch7-15.html" ><strong aria-hidden="true">7.15.</strong> 补充几点</a>
|
||
</li>
|
||
</ol>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch8/ch8.html" ><strong aria-hidden="true">8.</strong> Goroutines和Channels</a>
|
||
</li>
|
||
<ol class="section">
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch8/ch8-01.html" ><strong aria-hidden="true">8.1.</strong> Goroutines</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch8/ch8-02.html" ><strong aria-hidden="true">8.2.</strong> 示例: 并发的Clock服务</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch8/ch8-03.html" ><strong aria-hidden="true">8.3.</strong> 示例: 并发的Echo服务</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch8/ch8-04.html" ><strong aria-hidden="true">8.4.</strong> Channels</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch8/ch8-05.html" ><strong aria-hidden="true">8.5.</strong> 并发的循环</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch8/ch8-06.html" ><strong aria-hidden="true">8.6.</strong> 示例: 并发的Web爬虫</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch8/ch8-07.html" ><strong aria-hidden="true">8.7.</strong> 基于select的多路复用</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch8/ch8-08.html" ><strong aria-hidden="true">8.8.</strong> 示例: 并发的目录遍历</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch8/ch8-09.html" ><strong aria-hidden="true">8.9.</strong> 并发的退出</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch8/ch8-10.html" ><strong aria-hidden="true">8.10.</strong> 示例: 聊天服务</a>
|
||
</li>
|
||
</ol>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch9/ch9.html" ><strong aria-hidden="true">9.</strong> 基于共享变量的并发</a>
|
||
</li>
|
||
<ol class="section">
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch9/ch9-01.html" ><strong aria-hidden="true">9.1.</strong> 竞争条件</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch9/ch9-02.html" ><strong aria-hidden="true">9.2.</strong> sync.Mutex互斥锁</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch9/ch9-03.html" ><strong aria-hidden="true">9.3.</strong> sync.RWMutex读写锁</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch9/ch9-04.html" ><strong aria-hidden="true">9.4.</strong> 内存同步</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch9/ch9-05.html" ><strong aria-hidden="true">9.5.</strong> sync.Once惰性初始化</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch9/ch9-06.html" ><strong aria-hidden="true">9.6.</strong> 竞争条件检测</a>
|
||
</li>
|
||
<li class="chapter-item expanded ">
|
||
<a href="../ch9/ch9-07.html" ><strong aria-hidden="true">9.7.</strong> 示例: 并发的非阻塞缓存</a>
|
||
</li>
|
||
<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>
|
||
</li>
|
||
<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" class="active"><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" ><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>
|
||
</li>
|
||
</ol>
|
||
</ol>
|
||
|
||
</div>
|
||
<div id="sidebar-resize-handle" class="sidebar-resize-handle"></div>
|
||
</nav>
|
||
|
||
<div id="page-wrapper" class="page-wrapper">
|
||
|
||
<div class="page">
|
||
<div id="menu-bar-hover-placeholder"></div>
|
||
<div id="menu-bar" class="menu-bar sticky bordered">
|
||
<div class="left-buttons">
|
||
<button id="sidebar-toggle" class="icon-button" type="button" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
|
||
<i class="fa fa-bars"></i>
|
||
</button>
|
||
<button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
|
||
<i class="fa fa-paint-brush"></i>
|
||
</button>
|
||
<ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
|
||
<li role="none"><button role="menuitem" class="theme" id="light">Light (default)</button></li>
|
||
<li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
|
||
<li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
|
||
<li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
|
||
</ul>
|
||
</div>
|
||
|
||
<h1 class="menu-title"><a href="../index.html">Go语言圣经</a></h1>
|
||
|
||
<div class="right-buttons">
|
||
<a href="https://github.com/gopl-zh/gopl-zh.github.com" title="Git repository" aria-label="Git repository">
|
||
<i id="git-repository-button" class="fa fa-github"></i>
|
||
</a>
|
||
<a href="https://github.com/gopl-zh/gopl-zh.github.com/edit/master/ch12/ch12-05.md" title="Suggest an edit" aria-label="Suggest an edit">
|
||
<i id="git-edit-button" class="fa fa-edit"></i>
|
||
</a>
|
||
</div>
|
||
</div>
|
||
|
||
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
|
||
<script type="text/javascript">
|
||
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
|
||
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
|
||
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
|
||
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
|
||
});
|
||
</script>
|
||
|
||
<div id="content" class="content">
|
||
<!-- Page table of contents -->
|
||
<div class="sidetoc"><nav class="pagetoc"></nav></div>
|
||
|
||
<main>
|
||
<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>12.5. 通过reflect.Value修改值</h2>
|
||
<p>到目前为止，反射还只是程序中变量的另一种读取方式。然而，在本节中我们将重点讨论如何通过反射机制来修改变量。</p>
|
||
<p>回想一下，Go语言中类似x、x.f[1]和*p形式的表达式都可以表示变量，但是其它如x + 1和f(2)则不是变量。一个变量就是一个可寻址的内存空间，里面存储了一个值，并且存储的值可以通过内存地址来更新。</p>
|
||
<p>对于reflect.Values也有类似的区别。有一些reflect.Values是可取地址的；其它一些则不可以。考虑以下的声明语句：</p>
|
||
<pre><code class="language-Go">x := 2 // value type variable?
|
||
a := reflect.ValueOf(2) // 2 int no
|
||
b := reflect.ValueOf(x) // 2 int no
|
||
c := reflect.ValueOf(&x) // &x *int no
|
||
d := c.Elem() // 2 int yes (x)
|
||
</code></pre>
|
||
<p>其中a对应的变量不可取地址。因为a中的值仅仅是整数2的拷贝副本。b中的值也同样不可取地址。c中的值还是不可取地址，它只是一个指针<code>&x</code>的拷贝。实际上，所有通过reflect.ValueOf(x)返回的reflect.Value都是不可取地址的。但是对于d，它是c的解引用方式生成的，指向另一个变量，因此是可取地址的。我们可以通过调用reflect.ValueOf(&x).Elem()，来获取任意变量x对应的可取地址的Value。</p>
|
||
<p>我们可以通过调用reflect.Value的CanAddr方法来判断其是否可以被取地址：</p>
|
||
<pre><code class="language-Go">fmt.Println(a.CanAddr()) // "false"
|
||
fmt.Println(b.CanAddr()) // "false"
|
||
fmt.Println(c.CanAddr()) // "false"
|
||
fmt.Println(d.CanAddr()) // "true"
|
||
</code></pre>
|
||
<p>每当我们通过指针间接地获取的reflect.Value都是可取地址的，即使开始的是一个不可取地址的Value。在反射机制中，所有关于是否支持取地址的规则都是类似的。例如，slice的索引表达式e[i]将隐式地包含一个指针，它就是可取地址的，即使开始的e表达式不支持也没有关系。以此类推，reflect.ValueOf(e).Index(i)对应的值也是可取地址的，即使原始的reflect.ValueOf(e)不支持也没有关系。</p>
|
||
<p>要从变量对应的可取地址的reflect.Value来访问变量需要三个步骤。第一步是调用Addr()方法，它返回一个Value，里面保存了指向变量的指针。然后是在Value上调用Interface()方法，也就是返回一个interface{}，里面包含指向变量的指针。最后，如果我们知道变量的类型，我们可以使用类型的断言机制将得到的interface{}类型的接口强制转为普通的类型指针。这样我们就可以通过这个普通指针来更新变量了：</p>
|
||
<pre><code class="language-Go">x := 2
|
||
d := reflect.ValueOf(&x).Elem() // d refers to the variable x
|
||
px := d.Addr().Interface().(*int) // px := &x
|
||
*px = 3 // x = 3
|
||
fmt.Println(x) // "3"
|
||
</code></pre>
|
||
<p>或者，不使用指针，而是通过调用可取地址的reflect.Value的reflect.Value.Set方法来更新对应的值：</p>
|
||
<pre><code class="language-Go">d.Set(reflect.ValueOf(4))
|
||
fmt.Println(x) // "4"
|
||
</code></pre>
|
||
<p>Set方法将在运行时执行和编译时进行类似的可赋值性约束的检查。以上代码，变量和值都是int类型，但是如果变量是int64类型，那么程序将抛出一个panic异常，所以关键问题是要确保改类型的变量可以接受对应的值：</p>
|
||
<pre><code class="language-Go">d.Set(reflect.ValueOf(int64(5))) // panic: int64 is not assignable to int
|
||
</code></pre>
|
||
<p>同样，对一个不可取地址的reflect.Value调用Set方法也会导致panic异常：</p>
|
||
<pre><code class="language-Go">x := 2
|
||
b := reflect.ValueOf(x)
|
||
b.Set(reflect.ValueOf(3)) // panic: Set using unaddressable value
|
||
</code></pre>
|
||
<p>这里有很多用于基本数据类型的Set方法：SetInt、SetUint、SetString和SetFloat等。</p>
|
||
<pre><code class="language-Go">d := reflect.ValueOf(&x).Elem()
|
||
d.SetInt(3)
|
||
fmt.Println(x) // "3"
|
||
</code></pre>
|
||
<p>从某种程度上说，这些Set方法总是尽可能地完成任务。以SetInt为例，只要变量是某种类型的有符号整数就可以工作，即使是一些命名的类型、甚至只要底层数据类型是有符号整数就可以，而且如果对于变量类型值太大的话会被自动截断。但需要谨慎的是：对于一个引用interface{}类型的reflect.Value调用SetInt会导致panic异常，即使那个interface{}变量对于整数类型也不行。</p>
|
||
<pre><code class="language-Go">x := 1
|
||
rx := reflect.ValueOf(&x).Elem()
|
||
rx.SetInt(2) // OK, x = 2
|
||
rx.Set(reflect.ValueOf(3)) // OK, x = 3
|
||
rx.SetString("hello") // panic: string is not assignable to int
|
||
rx.Set(reflect.ValueOf("hello")) // panic: string is not assignable to int
|
||
|
||
var y interface{}
|
||
ry := reflect.ValueOf(&y).Elem()
|
||
ry.SetInt(2) // panic: SetInt called on interface Value
|
||
ry.Set(reflect.ValueOf(3)) // OK, y = int(3)
|
||
ry.SetString("hello") // panic: SetString called on interface Value
|
||
ry.Set(reflect.ValueOf("hello")) // OK, y = "hello"
|
||
</code></pre>
|
||
<p>当我们用Display显示os.Stdout结构时，我们发现反射可以越过Go语言的导出规则的限制读取结构体中未导出的成员，比如在类Unix系统上os.File结构体中的fd int成员。然而，利用反射机制并不能修改这些未导出的成员：</p>
|
||
<pre><code class="language-Go">stdout := reflect.ValueOf(os.Stdout).Elem() // *os.Stdout, an os.File var
|
||
fmt.Println(stdout.Type()) // "os.File"
|
||
fd := stdout.FieldByName("fd")
|
||
fmt.Println(fd.Int()) // "1"
|
||
fd.SetInt(2) // panic: unexported field
|
||
</code></pre>
|
||
<p>一个可取地址的reflect.Value会记录一个结构体成员是否是未导出成员，如果是的话则拒绝修改操作。因此，CanAddr方法并不能正确反映一个变量是否是可以被修改的。另一个相关的方法CanSet是用于检查对应的reflect.Value是否是可取地址并可被修改的：</p>
|
||
<pre><code class="language-Go">fmt.Println(fd.CanAddr(), fd.CanSet()) // "true false"
|
||
</code></pre>
|
||
|
||
|
||
<hr><table><tr><td><img width="222px" src="https://chai2010.cn/advanced-go-programming-book/css.png"></td><td><img width="222px" src="https://chai2010.cn/advanced-go-programming-book/cch.png"></td></tr></table>
|
||
|
||
|
||
<div id="giscus-container"></div>
|
||
|
||
|
||
|
||
<footer class="page-footer">
|
||
<span>© 2015-2016 | <a href="https://github.com/gopl-zh"> Go语言圣经中文版</a>, 仅学习交流使用</span>
|
||
</footer>
|
||
|
||
</main>
|
||
|
||
<nav class="nav-wrapper" aria-label="Page navigation">
|
||
<!-- Mobile navigation buttons -->
|
||
|
||
<a rel="prev" href="../ch12/ch12-04.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
||
<i class="fa fa-angle-left"></i>
|
||
</a>
|
||
|
||
|
||
<!-- ../ch12/ch12-06.html -->
|
||
<a rel="next" href="../ch12/ch12-06.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
||
<i class="fa fa-angle-right"></i>
|
||
</a>
|
||
|
||
<div style="clear: both"></div>
|
||
</nav>
|
||
</div>
|
||
</div>
|
||
|
||
<nav class="nav-wide-wrapper" aria-label="Page navigation">
|
||
|
||
<a rel="prev" href="../ch12/ch12-04.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
||
<i class="fa fa-angle-left"></i>
|
||
</a>
|
||
|
||
|
||
<a rel="next" href="../ch12/ch12-06.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
||
<i class="fa fa-angle-right"></i>
|
||
</a>
|
||
|
||
</nav>
|
||
|
||
</div>
|
||
|
||
<script type="text/javascript">
|
||
window.playground_copyable = true;
|
||
</script>
|
||
<script src="../static/wabook/mark.min.js" type="text/javascript" charset="utf-8"></script>
|
||
<script src="../static/wabook/clipboard.min.js" type="text/javascript" charset="utf-8"></script>
|
||
<script src="../static/wabook/highlight.js" type="text/javascript" charset="utf-8"></script>
|
||
<script src="../static/wabook/book.js" type="text/javascript" charset="utf-8"></script>
|
||
|
||
<script type="text/javascript" charset="utf-8">
|
||
var pagePath = "ch12/ch12-05.md"
|
||
</script>
|
||
|
||
<!-- Custom JS scripts -->
|
||
|
||
<script src="../static/wabook/giscus.js" type="text/javascript" charset="utf-8"></script>
|
||
|
||
|
||
</body>
|
||
</html>
|