PHP namespace (namespace)
这篇文章介绍的内容是关于PHP命名空间(namespace) ，有着一定的参考价值，现在分享给大家，有需要的朋友可以参考一下
命名空间概述
什么是命名空间?从广义上来说，命名空间是封装事物的一种方法。在很多地方可以见到这种抽象的概念。例如，在操作系统中目录用来将相关文件分组，对于目录中的文件来说，它就扮演了命名空间的角色。具体举个例子，文件 foo.txt 可以同时在目录/home/greg 和 /home/other 中存在，但在同一个目录中不能存在两个 foo.txt 文件。另外，在目录 /home/greg 外访问 foo.txt 文件时，我们必须将目录名以及目录分隔符放在文件名之前得到 /home/greg/foo.txt。这个原理应用到程序设计领域就是命名空间的概念。
在PHP中，命名空间用来解决在编写类库或应用程序时创建可重用的代码如类或函数时碰到的两类问题：
用户编写的代码与PHP内部的类/函数/常量或第三方类/函数/常量之间的名字冲突。 为很长的标识符名称(通常是为了缓解第一类问题而定义的)创建一个别名（或简短）的名称，提高源代码的可读性。
名空间提供了一种将相关的类、函数和常量组合到一起的途径。下面是一个说明 PHP 命名空间语法的示例：
我的项目目录结构如下: 
在index.php需要同时使用test1\Test.php和test2\Test.php,如果不用命名空间，由于两个类都同名，则会报错。
vendor\test1\Test.php
<?php
namespace vendor\test1;
class Test{
public function path(){
echo __DIR__."<br>";
}
}vendor\test2\Test.php
<?php
namespace vendor\test2;
class Test{
public function path(){
echo __DIR__."<br>";
}
}index.php
<?php
spl_autoload_register(function($class){
if($class){
$file = str_replace('\\','/',$class);
$file .= '.php';
if(file_exists($file)){
include($file);
}
}
});
$test = new \vendor\test1\Test();
$test->path();
$test2 = new \vendor\test2\Test();
$test2->path();输出如下:
D:\www\learning\vendor\test1 D:\www\learning\vendor\test2
全局命名空间
如果没有定义任何命名空间，所有的类与函数的定义都是在全局空间，与 PHP 引入命名空间概念前一样。在名称前加上前缀 \ 表示该名称是全局空间中的名称，即使该名称位于其它的命名空间中时也是如此。
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