(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
.
$a = new \currentnamespace\foo();
or
\currentnamespace\foo::staticmethod();
. This always resolves
to the literal name specified in the code, currentnamespace\foo
.
Here is an example of the three kinds of syntax in actual code:
file1.php
<?phpnamespace Foo\Bar\subnamespace;const FOO = 1;function foo() {}class foo{ static function staticmethod() {}}?>
file2.php
<?phpnamespace Foo\Bar;include 'file1.php';const FOO = 2;function foo() {}class foo{ static function staticmethod() {}}/* Unqualified name */foo(); // resolves to function Foo\Bar\foofoo::staticmethod(); // resolves to class Foo\Bar\foo, method staticmethodecho FOO; // resolves to constant Foo\Bar\FOO/* Qualified name */subnamespace\foo(); // resolves to function Foo\Bar\subnamespace\foosubnamespace\foo::staticmethod(); // resolves to class Foo\Bar\subnamespace\foo, // method staticmethodecho subnamespace\FOO; // resolves to constant Foo\Bar\subnamespace\FOO /* Fully qualified name */\Foo\Bar\foo(); // resolves to function Foo\Bar\foo\Foo\Bar\foo::staticmethod(); // resolves to class Foo\Bar\foo, method staticmethodecho \Foo\Bar\FOO; // resolves to constant Foo\Bar\FOO?>
Note that to access any global
class, function or constant, a fully qualified name can be used, such as
\strlen() or \Exception or
\INI_ALL
.
Example #1 Accessing global classes, functions and constants from within a namespace
<?phpnamespace Foo;function strlen() {}const INI_ALL = 3;class Exception {}$a = \strlen('hi'); // calls global function strlen$b = \INI_ALL; // accesses global constant INI_ALL$c = new \Exception('error'); // instantiates global class Exception?>