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Namespaces overview
(PHP 5 >= 5.3.0, PHP 7)
What are namespaces? In the broadest definition namespaces are a way of encapsulating items. This can be seen as an abstract concept in many places. For example, in any operating system directories serve to group related files, and act as a namespace for the files within them. As a concrete example, the file foo.txt can exist in both directory /home/greg and in /home/other, but two copies of foo.txt cannot co-exist in the same directory. In addition, to access the foo.txt file outside of the /home/greg directory, we must prepend the directory name to the file name using the directory separator to get /home/greg/foo.txt. This same principle extends to namespaces in the programming world.
| Version | Description |
|---|---|
| 7.0.0 | Added Group use Declarations. |
In the PHP world, namespaces are designed to solve two problems that authors of libraries and applications encounter when creating re-usable code elements such as classes or functions:
- Name collisions between code you create, and internal PHP classes/functions/constants or third-party classes/functions/constants.
- Ability to alias (or shorten) Extra_Long_Names designed to alleviate the first problem, improving readability of source code.
PHP Namespaces provide a way in which to group related classes, interfaces, functions and constants. Here is an example of namespace syntax in PHP:
Example #1 Namespace syntax example
<?php
namespace my\name; // see "Defining Namespaces" section
class MyClass {}
function myfunction() {}
const MYCONST = 1;
$a = new MyClass;
$c = new \my\name\MyClass; // see "Global Space" section
$a = strlen('hi'); // see "Using namespaces: fallback to global
// function/constant" section
$d = namespace\MYCONST; // see "namespace operator and __NAMESPACE__
// constant" section
$d = __NAMESPACE__ . '\MYCONST';
echo constant($d); // see "Namespaces and dynamic language features" section
?>
Note: Namespace names are case-insensitive.
Note:
The Namespace name PHP, and compound names starting with this name (like PHP\Classes) are reserved for internal language use and should not be used in the userspace code.
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Document created the 30/01/2003, last modified the 26/10/2018
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References
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