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PHP 5.3中的命名空间使用方法浅述

Jun 13, 2016 am 11:03 AM
name php Instructions name characteristic of space important

PHP 5.3 的一个新的重要特性就是 命名空间(namespace)。

这一特性在 PHP5.0x 时候就提出过,后来被取消并安排在 PHP6 中实现。而此次又再次“提前”到了 PHP 5.3 发布,可见开发人员对其的重视以及谨慎的态度。

官方发布时说明文档的内容可能已过期(documentation maybe out dated),所以在这里简单的说明命名空间的用法:首先是声明一个命名空间,加入了新的关键字 namespace ,其应在类文件的开头

<ol class="dp-c">
<li class="alt"><span><span><?php  </SPAN></span><li class=""><span>namespace Project::Module;   </span></li>
<li class="alt"><span> </span></li>
<li class="">
<span></span><span class="keyword"><strong><font color="#006699">class</font></strong></span><span> User {  </span>
</li></span></li>
<li class="alt">
<span></span><span class="keyword"><strong><font color="#006699">const</font></strong></span><span> STATUS_OK = true;  </span>
</li>
<li class=""><span> </span></li>
<li class="alt">
<span></span><span class="keyword"><strong><font color="#006699">function</font></strong></span><span> register(</span><span class="vars"><font color="#dd0000">$data</font></span><span>) {  </span>
</li>
<li class=""><span>...  </span></li>
<li class="alt"><span>}  </span></li>
<li class=""><span> </span></li>
<li class="alt"><span>...  </span></li>
<li class=""><span>}  </span></li>
</ol>
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然后在控制器中(可能是其他文件)就可以这样调用

<ol class="dp-c">
<li class="alt"><span><span class="vars"><font color="#dd0000">$user</font></span><span> = </span><span class="keyword"><strong><font color="#006699">new</font></strong></span><span> Project::Module::User();   </span></span></li>
<li class="">
<span></span><span class="vars"><font color="#dd0000">$user</font></span><span>->register(</span><span class="vars"><font color="#dd0000">$register_info</font></span><span>); </span>
</li>
</ol>
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的确与平常的并无两样,但是我们可以将两个相互独立的类联系起来。比如

<ol class="dp-c">
<li class="alt"><span><span>Project::Module::User;   </span></span></li>
<li class=""><span>Project::Module::Blog;  </span></li>
</ol>
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这样就能从语言本身更容易描述和理解变量、类之间的关系,从而避免了“传统”上的 Project_Module_Blog 这样冗长的命名方式。

上面的说明可能很难说明使用命名空间带来了什么好处,新增加的 use 和 as 关键字或许能更好的说明问题。use 和 as 语句可以引用和声明 命名空间的“别名”。比如,上述的控制器中实例化类的代码可以这样写

<ol class="dp-c">
<li class="alt"><span><span class="keyword"><strong><font color="#006699">use</font></strong></span><span> Project::Module;  </span></span></li>
<li class="">
<span></span><span class="vars"><font color="#dd0000">$user</font></span><span> = </span><span class="keyword"><strong><font color="#006699">new</font></strong></span><span> Module::User();   </span>
</li>
<li class="alt">
<span></span><span class="vars"><font color="#dd0000">$user</font></span><span>->register(</span><span class="vars"><font color="#dd0000">$register_info</font></span><span>);  </span>
</li>
</ol>
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甚至

<ol class="dp-c">
<li class="alt"><span><span class="keyword"><strong><font color="#006699">use</font></strong></span><span> Project::Module::User </span><span class="keyword"><strong><font color="#006699">as</font></strong></span><span> ModuleUser;  </span></span></li>
<li class="">
<span></span><span class="vars"><font color="#dd0000">$user</font></span><span> = </span><span class="keyword"><strong><font color="#006699">new</font></strong></span><span> ModuleUser;   </span>
</li>
<li class="alt">
<span></span><span class="vars"><font color="#dd0000">$user</font></span><span>->register(</span><span class="vars"><font color="#dd0000">$register_info</font></span><span>);  </span>
</li>
</ol>
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类中的常量也可以通过命名空间访问,比如上述类中的 STATUS_OK 就可以通过命名空间

<ol class="dp-c"><li class="alt"><span><span>Project::Module::User::STATUS_OK  </span></span></li></ol>
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访问。进一步的,也可以用别名简化那么长的“变量名称”

<ol class="dp-c">
<li class="alt"><span><span class="keyword"><strong><font color="#006699">use</font></strong></span><span> Project::Module::User::STATUS_OK </span><span class="keyword"><strong><font color="#006699">as</font></strong></span><span> STATUS_OK;  </span></span></li>
<li class="">
<span></span><span class="func">echo</span><span> STATUS_OK;  </span>
</li>
</ol>
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顺便提下“超空间(The Global Namespace)”的概念。所谓的“超空间”,就是没有指定命名空间的变量、类和函数。比如

<ol class="dp-c">
<li class="alt"><span><span class="keyword"><strong><font color="#006699">function</font></strong></span><span> foo() {  </span></span></li>
<li class=""><span>...  </span></li>
<li class="alt"><span>}  </span></li>
</ol>
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这的函数,可以使用 foo() 执行的同时,也可以使用 ::foo(); 这样执行。

最后,配合使用 autoload 函数即可载入指定命名空间的类。简单的函数如下

<ol class="dp-c">
<li class="alt"><span><span class="keyword"><strong><font color="#006699">function</font></strong></span><span> __autoload( </span><span class="vars"><font color="#dd0000">$classname</font></span><span> ) {  </span></span></li>
<li class="">
<span></span><span class="vars"><font color="#dd0000">$classname</font></span><span> = </span><span class="func">strtolower</span><span>( </span><span class="vars"><font color="#dd0000">$classname</font></span><span> );  </span>
</li>
<li class="alt">
<span></span><span class="vars"><font color="#dd0000">$classname</font></span><span> = </span><span class="func">str_replace</span><span>( </span><span class="string"><font color="#0000ff">'::'</font></span><span>, DIRECTORY_SEPARATOR, </span><span class="vars"><font color="#dd0000">$classname</font></span><span> );  </span>
</li>
<li class="">
<span></span><span class="keyword"><strong><font color="#006699">require_once</font></strong></span><span>( dirname( </span><span class="keyword"><strong><font color="#006699">__FILE__</font></strong></span><span> ) . </span><span class="string"><font color="#0000ff">'/'</font></span><span> . </span><span class="vars"><font color="#dd0000">$classname</font></span><span> . </span><span class="string"><font color="#0000ff">'.class.php'</font></span><span> );  </span>
</li>
<li class="alt"><span>}  </span></li>
</ol>
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这样,比如调用

<ol class="dp-c"><li class="alt"><span><span>__autoload(</span><span class="string"><font color="#0000ff">'Project::Module::User'</font></span><span>);  </span></span></li></ol>
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就可以自动载入 Project_Module_User.class.php 文件(虽然这样看起来并不方便多少)。


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