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.
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:
PHP Namespaces provide a way in which to group related classes, 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
?>
Namespaces are available in PHP as of PHP 5.3.0.