命名空间与自动加载系列(四)--命名空间中的常量与函数
常量与函数不受命名空间的影响。
为了方便理解，直接使用代码示例，现在来新建目录与文件：
<span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(0, 0, 0)">demo</span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(0, 0, 0)">index</span>.<span style="box-sizing: border-box;color: rgb(0, 0, 0)">php</span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(0, 0, 0)">test</span>.<span style="box-sizing: border-box;color: rgb(0, 0, 0)">php</span></span>
demo目录下有两个文件，分别是
index.php与test.php，下面来编写这两个文件
<span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(170, 85, 0)">// test.php</span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(152, 26, 26)"><?</span><span style="box-sizing: border-box;color: rgb(0, 0, 0)">php</span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(170, 85, 0)">// 公共函数</span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(119, 0, 136)">function</span> <span style="box-sizing: border-box;color: rgb(0, 0, 255)">say</span>() {</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(119, 0, 136)">echo</span> <span style="box-sizing: border-box;color: rgb(170, 17, 17)">'hi php'</span> . <span style="box-sizing: border-box;color: rgb(0, 0, 0)">PHP_EOL</span>;</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">}</span>
<span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(170, 85, 0)">// index.php</span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(152, 26, 26)"><?</span><span style="box-sizing: border-box;color: rgb(0, 0, 0)">php</span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(119, 0, 136)">namespace</span> <span style="box-sizing: border-box;color: rgb(0, 0, 255)">App</span>;</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(119, 0, 136)">include</span> <span style="box-sizing: border-box;color: rgb(170, 17, 17)">'./test.php'</span>;</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(0, 0, 0)">say</span>();</span>
函数的特殊性
现在开始运行index.php，打印出来的结果是hi php。index.php中引入了不带命名空间的test.php，并且输出了test.php文件中say方法中的内容。
下面再来改造一下index.php，为其添加一个函数，如下：
<span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(152, 26, 26)"><?</span><span style="box-sizing: border-box;color: rgb(0, 0, 0)">php</span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(119, 0, 136)">namespace</span> <span style="box-sizing: border-box;color: rgb(0, 0, 255)">App</span>;</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(119, 0, 136)">include</span> <span style="box-sizing: border-box;color: rgb(170, 17, 17)">'./test.php'</span>;</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(119, 0, 136)">function</span> <span style="box-sizing: border-box;color: rgb(0, 0, 255)">say</span>() {</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(119, 0, 136)">echo</span> <span style="box-sizing: border-box;color: rgb(170, 17, 17)">'index.php中的say'</span> . <span style="box-sizing: border-box;color: rgb(0, 0, 0)">PHP_EOL</span>;</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px">}</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(0, 0, 0)">say</span>();</span>
运行后得到输出的结果index.php中的say。
由此可以得出，函数不受命名空间的影响，是全局作用的。当命名空间中有同名函数，则优先使用命名空间中的函数。
常量的特殊性
注释两个文件中的代码，从新开始
<span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(170, 85, 0)">// test.php</span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(152, 26, 26)"><?</span><span style="box-sizing: border-box;color: rgb(0, 0, 0)">php</span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(51, 0, 170)">define</span>(<span style="box-sizing: border-box;color: rgb(170, 17, 17)">'NAME'</span>,<span style="box-sizing: border-box;color: rgb(170, 17, 17)">'自如初'</span>);</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(119, 0, 136)">const</span> <span style="box-sizing: border-box;color: rgb(0, 0, 0)">WEB_URL</span> <span style="box-sizing: border-box;color: rgb(152, 26, 26)">=</span> <span style="box-sizing: border-box;color: rgb(170, 17, 17)">'www.ziruchu.com'</span>;</span>
<span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(170, 85, 0)">// index.php</span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(152, 26, 26)"><?</span><span style="box-sizing: border-box;color: rgb(0, 0, 0)">php</span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(119, 0, 136)">namespace</span> <span style="box-sizing: border-box;color: rgb(0, 0, 255)">App</span>;</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(119, 0, 136)">include</span> <span style="box-sizing: border-box;color: rgb(170, 17, 17)">'./test.php'</span>;</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(119, 0, 136)">echo</span> <span style="box-sizing: border-box;color: rgb(0, 0, 0)">NAME</span>;</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(119, 0, 136)">echo</span> <span style="box-sizing: border-box;color: rgb(0, 0, 0)">WEB_URL</span>;</span>
运行index.php，输出了两个常量的值。现在为test.php添加命名空间
<span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(152, 26, 26)"><?</span><span style="box-sizing: border-box;color: rgb(0, 0, 0)">php</span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(119, 0, 136)">namespace</span> <span style="box-sizing: border-box;color: rgb(0, 0, 255)">Common</span>;</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(51, 0, 170)">define</span>(<span style="box-sizing: border-box;color: rgb(170, 17, 17)">'NAME'</span>,<span style="box-sizing: border-box;color: rgb(170, 17, 17)">'自如初'</span>);</span><br></br><span style="box-sizing: border-box;padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(119, 0, 136)">const</span> <span style="box-sizing: border-box;color: rgb(0, 0, 0)">WEB_URL</span> <span style="box-sizing: border-box;color: rgb(152, 26, 26)">=</span> <span style="box-sizing: border-box;color: rgb(170, 17, 17)">'www.ziruchu.com'</span>;</span>
再次运行index.php文件，会发现常量NAME的值被输出了，而通过const定义的常量WEB_URL报错了，Fatal error: Uncaught Error: Undefined constant "App\WEB_URL"。通过这个案例可以看到，define与const是有所区别的。
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