Why use namespaces? As the number of files in the project increases, it is inevitable that class names, function names, and constant names will be repeated. This article mainly shares with you an introduction to PHP namespaces, hoping to help everyone.

未定义命名空间的如下图

Fatal error: Cannot redeclare class test in E:\PHP\PHPTutorial\WWW\demo\namespace\b.php on line 2

How to use namespace

Define three files

a.php

namespace a\b;

class test{    public function show(){        echo 'this is a';    }}

b.php

index.php
require './a.php';
require './b.php';
$a = new a\b\test ();When instantiating a class, remember to add the namespace
Import the namespace
Since it is more cumbersome every time to instantiate the class, you can use the second way of writing
ba0bf9f6a66d5f65ad2b51a4d38cbdb0show();
1. The overall import of the space requires an alias. If there is no alias, the character after the last \ is used as the space name by default 
Global space
The code behind namespace All belong to the current space, and the code outside the namespace belongs to the global space.
How to use the global space in the current space, just add \ backslash after the required members to indicate the global space. 
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