The namespace keyword and __NAMESPACE__ magic 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 ""
    ?>
    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
    ?>

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    User Contributed Notes 2 notes

    up
    88
    a dot schaffhirt at sedna-soft dot de
    14 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
    ?>

    Hope, this can save someone from some trouble.

    Best regards.
    up
    0
    bharatthapa45 at gmail dot com
    2 years ago
    Difference between __NAMESPACE__ and keyword 'namespace' that I find relevant is when invoking a class:

    <?php
    namespace MyApp;

    class     App {
    static function     app(){
    echo     'hello app';
    }
    }

    // this will work:
    $obj = new namespace\App::app();

    // this will not work
    $obj = new __NAMESPACE__\App::app();

    // however this will work:
    $obj = __NAMESPACE__ . '\App';
    $obj::foo();

    ?>
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