Detailed explanation of PHP namespace namespace definition

In PHP, functions or classes with the same name are not allowed. In order to prevent repeated conflicts in class names or function names defined by programmers in the project, the concept of namespace was introduced in PHP5.3.

1. Namespace means dividing the code into different spaces. The class names in different spaces are independent of each other and do not conflict with each other. Multiple namespaces can exist in a php file, and there cannot be any code before the first namespace. The code after the content space declaration belongs to this namespace , for example:

<?php
echo 111;  //由于namespace前有代码而报错
namespace Teacher;
class Person{
  function __construct(){
   echo &#39;Please study!&#39;;
  }
}

2. When calling classes or methods in different spaces, the namespace must be specified . For example:

<?php
namespace Teacher;
class Person{
  function __construct(){
   echo &#39;Please study!<br/>&#39;;
  }
}
function Person(){
  return &#39;You must stay here!&#39;;
};
namespace Student;
class Person{
  function __construct(){
   echo &#39;I want to play!<br/>&#39;;
  }
}
new Person();     //本空间（Student空间）
new \Teacher\Person();   //Teacher空间
new \Student\Person();   //Student空间
echo \Teacher\Person();   //Teacher空间下Person函数

Output:

I want to play!
Please study!
I want to play!
You must stay here!

3. In the namespace Other files imported into it will not belong to this namespace, but to the public space or the namespace defined in the file itself. Example:

First define a 1.php and 2.php file:

<?php  //1.php
class Person{
 function __construct(){
   echo &#39;I am one!<br/>&#39;;
  }
}

<?php
namespace Newer;
require_once &#39;./1.php&#39;;
new Person();  //报错，找不到Person;
new \Person();  //输出 I am tow!;

<?php  //2.php
namespace Two
class Person{
 function __construct(){
   echo &#39;I am tow!<br/>&#39;;
  }
}

<?php
namespace New;
require_once &#39;./2.php&#39;;
new Person();  //报错，(当前空间)找不到Person;
new \Person();  //报错，(公共空间)找不到Person;
new \Two\Person(); //输出 I am tow!;

4. Let’s look at how to use use: (use can be abbreviated for future references)

namespace School\Parents;
class Man{
  function __construct(){
   echo &#39;Listen to teachers!<br/>&#39;;
  }
}
namespace School\Teacher;
class Person{
  function __construct(){
   echo &#39;Please study!<br/>&#39;;
  }
}
namespace School\Student;
class Person{
  function __construct(){
   echo &#39;I want to play!<br/>&#39;;
  }
}
new Person();     //输出I want to play!
new \School\Teacher\Person(); //输出Please study!
new Teacher\Person();   //报错
----------
use School\Teacher;
new Teacher\Person();   //输出Please study!
----------
use School\Teacher as Tc;
new Tc\Person();   //输出Please study!
----------
use \School\Teacher\Person;
new Person();   //报错
----------
use \School\Parent\Man;
new Man();   //报错

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