(PHP 5 >= 5.3.0, PHP 7, PHP 8)
Before discussing the use of namespaces, it is important to understand how PHP knows which namespaced element your code is requesting. A simple analogy can be made between PHP namespaces and a filesystem. There are three ways to access a file in a file system:
foo.txt
. This resolves to currentdirectory/foo.txt
where currentdirectory
is the directory currently occupied. So if the current directory is /home/foo
, the name resolves to /home/foo/foo.txt
. subdirectory/foo.txt
. This resolves to currentdirectory/subdirectory/foo.txt
. /main/foo.txt
. This resolves to /main/foo.txt
. $a = new foo();
or foo::staticmethod();
. If the current namespace is currentnamespace
, this resolves to currentnamespace\foo
. If the code is global, non-namespaced code, this resolves to foo
. One caveat: unqualified names for functions and constants will resolve to global functions and constants if the namespaced function or constant is not defined. See Using namespaces: fallback to global function/constant for details. $a = new subnamespace\foo();
or subnamespace\foo::staticmethod();
. If the current namespace is currentnamespace
, this resolves to currentnamespace\subnamespace\foo
. If the code is global, non-namespaced code, this resolves to subnamespace\foo
. $a = new \currentnamespace\foo();
or \currentnamespace\foo::staticmethod();
. This always resolves to the literal name specified in the code, currentnamespace\foo
. Here is an example of the three kinds of syntax in actual code:
file1.php
<?php
namespace Foo\Bar\subnamespace;
const FOO = 1;
function foo() {}
class foo
{
static function staticmethod() {}
}
?>
file2.php
<?php
namespace Foo\Bar;
include 'file1.php';
const FOO = 2;
function foo() {}
class foo
{
static function staticmethod() {}
}
foo(); // resolves to function Foo\Bar\foo
foo::staticmethod(); // resolves to class Foo\Bar\foo, method staticmethod
echo FOO; // resolves to constant Foo\Bar\FOO
subnamespace\foo(); // resolves to function Foo\Bar\subnamespace\foo
subnamespace\foo::staticmethod(); // resolves to class Foo\Bar\subnamespace\foo,
Note that to access any global class, function or constant, a fully qualified name can be used, such as \strlen() or \Exception or \INI_ALL
.
Example #1 Accessing global classes, functions and constants from within a namespace
<?php
namespace Foo;
function strlen() {}
const INI_ALL = 3;
class Exception {}
$a = \strlen('hi'); // calls global function strlen
$b = \INI_ALL; // accesses global constant INI_ALL
$c = new \Exception('error'); // instantiates global class Exception
?>