namespace keyword and __NAMESPACE__ constant
(PHP 5 >= 5.3.0, PHP 7, PHP 8)
PHP supports two ways of abstractly accessing elements within the current namespace,
the __NAMESPACE__ magic constant, and the namespace
keyword.
The value of __NAMESPACE__ is a string that contains the current
namespace name. In global, un-namespaced code, it contains an empty string.
Example #1 __NAMESPACE__ example, namespaced code
<?php
namespace MyProject;
echo '"', __NAMESPACE__, '"'; // outputs "MyProject"
?>
Example #2 __NAMESPACE__ example, global code
<?php
echo '"', __NAMESPACE__, '"'; // outputs ""
?>
__NAMESPACE__ constant is useful for dynamically constructing
names, for instance:
Example #3 using __NAMESPACE__ for dynamic name construction
<?php
namespace MyProject;
function get($classname)
{
$a = __NAMESPACE__ . '\\' . $classname;
return new $a;
}
?>
The namespace keyword can be used to explicitly request
an element from the current namespace or a sub-namespace. It is the namespace
equivalent of the self operator for classes.
Example #4 the namespace operator, inside a namespace
<?php
namespace MyProject;
use blah\blah as mine; // see "Using namespaces: Aliasing/Importing"
blah\mine(); // calls function MyProject\blah\mine()
namespace\blah\mine(); // calls function MyProject\blah\mine()
namespace\func(); // calls function MyProject\func()
namespace\sub\func(); // calls function MyProject\sub\func()
namespace\cname::method(); // calls static method "method" of class MyProject\cname
$a = new namespace\sub\cname(); // instantiates object of class MyProject\sub\cname
$b = namespace\CONSTANT; // assigns value of constant MyProject\CONSTANT to $b
?>
Example #5 the namespace operator, in global code
<?php
namespace\func(); // calls function func()
namespace\sub\func(); // calls function sub\func()
namespace\cname::method(); // calls static method "method" of class cname
$a = new namespace\sub\cname(); // instantiates object of class sub\cname
$b = namespace\CONSTANT; // assigns value of constant CONSTANT to $b
?>
