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<ol class="chapter"><li class="chapter-item expanded affix "><a href="../index.html">Go语言圣经</a></li><li class="chapter-item expanded affix "><a href="../preface-zh.html">译者序</a></li><li class="chapter-item expanded affix "><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><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><li class="chapter-item expanded "><a href="../ch2/ch2.html"><strong aria-hidden="true">2.</strong> 程序结构</a></li><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><li class="chapter-item expanded "><a href="../ch3/ch3.html"><strong aria-hidden="true">3.</strong> 基础数据类型</a></li><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><li class="chapter-item expanded "><a href="../ch4/ch4.html"><strong aria-hidden="true">4.</strong> 复合数据类型</a></li><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</
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<li><em>KusonStack一站式可编程配置技术栈(Go): <a href="https://github.com/KusionStack/kusion">https://github.com/KusionStack/kusion</a></em></li>
<li><em>KCL 配置编程语言(Rust): <a href="https://github.com/KusionStack/KCLVM">https://github.com/KusionStack/KCLVM</a></em></li>
<li><em>凹语言™: <a href="https://github.com/wa-lang/wa">https://github.com/wa-lang/wa</a></em></li>
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<hr>
<h2 id="78-error接口"><a class="header" href="#78-error接口">7.8. error接口</a></h2>
<p>从本书的开始我们就已经创建和使用过神秘的预定义error类型而且没有解释它究竟是什么。实际上它就是interface类型这个类型有一个返回错误信息的单一方法</p>
<pre><code class="language-go">type error interface {
Error() string
}
</code></pre>
<p>创建一个error最简单的方法就是调用errors.New函数它会根据传入的错误信息返回一个新的error。整个errors包仅只有4行</p>
<pre><code class="language-go">package errors
func New(text string) error { return &amp;errorString{text} }
type errorString struct { text string }
func (e *errorString) Error() string { return e.text }
</code></pre>
<p>承载errorString的类型是一个结构体而非一个字符串这是为了保护它表示的错误避免粗心或有意的更新。并且因为是指针类型<code>*errorString</code>满足error接口而非errorString类型所以每个New函数的调用都分配了一个独特的和其他错误不相同的实例。我们也不想要重要的error例如io.EOF和一个刚好有相同错误消息的error比较后相等。</p>
<pre><code class="language-go">fmt.Println(errors.New(&quot;EOF&quot;) == errors.New(&quot;EOF&quot;)) // &quot;false&quot;
</code></pre>
<p>调用errors.New函数是非常稀少的因为有一个方便的封装函数fmt.Errorf它还会处理字符串格式化。我们曾多次在第5章中用到它。</p>
<pre><code class="language-go">package fmt
import &quot;errors&quot;
func Errorf(format string, args ...interface{}) error {
return errors.New(Sprintf(format, args...))
}
</code></pre>
<p>虽然<code>*errorString</code>可能是最简单的错误类型但远非只有它一个。例如syscall包提供了Go语言底层系统调用API。在多个平台上它定义一个实现error接口的数字类型Errno并且在Unix平台上Errno的Error方法会从一个字符串表中查找错误消息如下面展示的这样</p>
<pre><code class="language-go">package syscall
type Errno uintptr // operating system error code
var errors = [...]string{
1: &quot;operation not permitted&quot;, // EPERM
2: &quot;no such file or directory&quot;, // ENOENT
3: &quot;no such process&quot;, // ESRCH
// ...
}
func (e Errno) Error() string {
if 0 &lt;= int(e) &amp;&amp; int(e) &lt; len(errors) {
return errors[e]
}
return fmt.Sprintf(&quot;errno %d&quot;, e)
}
</code></pre>
<p>下面的语句创建了一个持有Errno值为2的接口值表示POSIX ENOENT状况</p>
<pre><code class="language-go">var err error = syscall.Errno(2)
fmt.Println(err.Error()) // &quot;no such file or directory&quot;
fmt.Println(err) // &quot;no such file or directory&quot;
</code></pre>
<p>err的值图形化的呈现在图7.6中。</p>
<p><img src="../images/ch7-06.png" alt="" /></p>
<p>Errno是一个系统调用错误的高效表示方式它通过一个有限的集合进行描述并且它满足标准的错误接口。我们会在第7.11节了解到其它满足这个接口的类型。</p>
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