namespace keyword and __NAMESPACE_

namespace keyword and NAMESPACE constant

(PHP 5 >= 5.3.0, PHP 7)

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 ""
?>

The __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
?>

User Contributed Notes

a dot schaffhirt at sedna-soft dot de

6 years ago


Just in case you wonder what the practical use of the namespace keyword is...

It can explicitly refer to classes from the current namespace regardless of possibly "use"d classes with the same name from other namespaces. However, this does not apply for functions.

Example:

<?php
namespace foo;
class Xyz {}
function abc () {}
?>

<?php
namespace bar;
class Xyz {}
function abc () {}
?>

<?php
namespace bar;
use foo|Xyz;
use foo|abc;
new Xyz(); // instantiates \foo\Xyz
new namespace|Xyz(); // instantiates \bar\Xyz
abc(); // invokes \bar\abc regardless of the second use statement
|foo|abc(); // it has to be invoked using the fully qualified name
?>

(Sorry, I had to use "|" instead of "\", as it was always discarded in the preview, except within a comment.)

Hope, this can save someone from some trouble.

Best regards.

namespace keyword and __NAMESPACE__ constant

User Contributed Notes

namespace keyword and NAMESPACE constant