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deploy: de40458a40ab5babf96252dae1f10d84b068ba16
2022-08-24 10:48:15 +00:00
<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>
deploy: 06a1bdf7353d7ab131c932b22e155c41f763dde3
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<hr>
<h2 id="72-接口类型"><a class="header" href="#72-接口类型">7.2. 接口类型</a></h2>
<p>接口类型具体描述了一系列方法的集合，一个实现了这些方法的具体类型是这个接口类型的实例。</p>
<p>io.Writer类型是用得最广泛的接口之一，因为它提供了所有类型的写入bytes的抽象，包括文件类型，内存缓冲区，网络链接，HTTP客户端，压缩工具，哈希等等。io包中定义了很多其它有用的接口类型。Reader可以代表任意可以读取bytes的类型，Closer可以是任意可以关闭的值，例如一个文件或是网络链接。（到现在你可能注意到了很多Go语言中单方法接口的命名习惯）</p>
<pre><code class="language-go">package io
type Reader interface {
Read(p []byte) (n int, err error)
}
type Closer interface {
Close() error
}
</code></pre>
<p>再往下看，我们发现有些新的接口类型通过组合已有的接口来定义。下面是两个例子：</p>
<pre><code class="language-go">type ReadWriter interface {
Reader
Writer
}
type ReadWriteCloser interface {
Reader
Writer
Closer
}
</code></pre>
<p>上面用到的语法和结构内嵌相似，我们可以用这种方式以一个简写命名一个接口，而不用声明它所有的方法。这种方式称为接口内嵌。尽管略失简洁，我们可以像下面这样，不使用内嵌来声明io.ReadWriter接口。</p>
<pre><code class="language-go">type ReadWriter interface {
Read(p []byte) (n int, err error)
Write(p []byte) (n int, err error)
}
</code></pre>
<p>或者甚至使用一种混合的风格：</p>
<pre><code class="language-go">type ReadWriter interface {
Read(p []byte) (n int, err error)
Writer
}
</code></pre>
<p>上面3种定义方式都是一样的效果。方法顺序的变化也没有影响，唯一重要的就是这个集合里面的方法。</p>
<p><strong>练习 7.4：</strong> strings.NewReader函数通过读取一个string参数返回一个满足io.Reader接口类型的值（和其它值）。实现一个简单版本的NewReader，用它来构造一个接收字符串输入的HTML解析器（§5.2）</p>
<p><strong>练习 7.5：</strong> io包里面的LimitReader函数接收一个io.Reader接口类型的r和字节数n，并且返回另一个从r中读取字节但是当读完n个字节后就表示读到文件结束的Reader。实现这个LimitReader函数：</p>
<pre><code class="language-go">func LimitReader(r io.Reader, n int64) io.Reader
</code></pre>
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