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Name resolution rules

(PHP 5 >= 5.3.0)

For the purposes of these resolution rules, here are some important definitions:

Namespace name definitions
Unqualified name

This is an identifier without a namespace separator, such as Foo

Qualified name

This is an identifier with a namespace separator, such as Foo\Bar

Fully qualified name

This is an identifier with a namespace separator that begins with a namespace separator, such as \Foo\Bar. The namespace \Foo is also a fully qualified name.

Names are resolved following these resolution rules:

  1. Calls to fully qualified functions, classes or constants are resolved at compile-time. For instance new \A\B resolves to class A\B.
  2. All unqualified and qualified names (not fully qualified names) are translated during compilation according to current import rules. For example, if the namespace A\B\C is imported as C, a call to C\D\e() is translated to A\B\C\D\e().
  3. Inside a namespace, all qualified names not translated according to import rules have the current namespace prepended. For example, if a call to C\D\e() is performed within namespace A\B, it is translated to A\B\C\D\e().
  4. Unqualified class names are translated during compilation according to current import rules (full name substituted for short imported name). In example, if the namespace A\B\C is imported as C, new C() is translated to new A\B\C().
  5. Inside namespace (say A\B), calls to unqualified functions are resolved at run-time. Here is how a call to function foo() is resolved:
    1. It looks for a function from the current namespace: A\B\foo().
    2. It tries to find and call the global function foo().
  6. Inside namespace (say A\B), calls to unqualified or qualified class names (not fully qualified class names) are resolved at run-time. Here is how a call to new C() or new D\E() is resolved. For new C():
    1. It looks for a class from the current namespace: A\B\C.
    2. It attempts to autoload A\B\C.
    For new D\E():
    1. It looks for a class by prepending the current namespace: A\B\D\E.
    2. It attempts to autoload A\B\D\E.
    To reference any global class in the global namespace, its fully qualified name new \C() must be used.

Exemplo #1 Name resolutions illustrated

<?php
namespace A;
use 
B\DC\as F;

// function calls

foo();      // first tries to call "foo" defined in namespace "A"
            // then calls global function "foo"

\foo();     // calls function "foo" defined in global scope

my\foo();   // calls function "foo" defined in namespace "A\my"

F();        // first tries to call "F" defined in namespace "A"
            // then calls global function "F"

// class references

new B();    // creates object of class "B" defined in namespace "A"
            // if not found, it tries to autoload class "A\B"

new D();    // using import rules, creates object of class "D" defined in namespace "B"
            // if not found, it tries to autoload class "B\D"

new F();    // using import rules, creates object of class "E" defined in namespace "C"
            // if not found, it tries to autoload class "C\E"

new \B();   // creates object of class "B" defined in global scope
            // if not found, it tries to autoload class "B"

new \D();   // creates object of class "D" defined in global scope
            // if not found, it tries to autoload class "D"

new \F();   // creates object of class "F" defined in global scope
            // if not found, it tries to autoload class "F"

// static methods/namespace functions from another namespace

B\foo();    // calls function "foo" from namespace "A\B"

B::foo();   // calls method "foo" of class "B" defined in namespace "A"
            // if class "A\B" not found, it tries to autoload class "A\B"

D::foo();   // using import rules, calls method "foo" of class "D" defined in namespace "B"
            // if class "B\D" not found, it tries to autoload class "B\D"

\B\foo();   // calls function "foo" from namespace "B"

\B::foo();  // calls method "foo" of class "B" from global scope
            // if class "B" not found, it tries to autoload class "B"

// static methods/namespace functions of current namespace

A\B::foo();   // calls method "foo" of class "B" from namespace "A\A"
              // if class "A\A\B" not found, it tries to autoload class "A\A\B"

\A\B::foo();  // calls method "foo" of class "B" from namespace "A"
              // if class "A\B" not found, it tries to autoload class "A\B"
?>
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User Contributed Notes 7 notes

up
10
kdimi
3 years ago
If you like to declare an __autoload function within a namespace or class, use the spl_autoload_register() function to register it and it will work fine.
up
8
rangel
5 years ago
The term "autoload" mentioned here shall not be confused with __autoload function to autoload objects. Regarding the __autoload and namespaces' resolution I'd like to share the following experience:

->Say you have the following directory structure:

- root
      | - loader.php
      | - ns
             | - foo.php

->foo.php

<?php
namespace ns;
class
foo
{
    public
$say;
   
    public function
__construct()
    {
       
$this->say = "bar";
    }
   
}
?>

-> loader.php

<?php
//GLOBAL SPACE <--
function __autoload($c)
{
    require_once
$c . ".php";
}

class
foo extends ns\foo // ns\foo is loaded here
{
    public function
__construct()
    {
       
parent::__construct();
        echo
"<br />foo" . $this->say;
    }
}
$a = new ns\foo(); // ns\foo also loads ns/foo.php just fine here.
echo $a->say;   // prints bar as expected.
$b = new foo// prints foobar just fine.
?>

If you keep your directory/file matching namespace/class consistence the object __autoload works fine.
But... if you try to give loader.php a namespace you'll obviously get fatal errors.
My sample is just 1 level dir, but I've tested with a very complex and deeper structure. Hope anybody finds this useful.

Cheers!
up
3
safakozpinar at NOSPAM dot gmail dot com
3 years ago
As working with namespaces and using (custom or basic) autoload structure; magic function __autoload must be defined in global scope, not in a namespace, also not in another function or method.

<?php
namespace Glue {
   
/**
     * Define your custom structure and algorithms
     * for autoloading in this class.
     */
   
class Import
   
{
        public static function
load ($classname)
        {
            echo
'Autoloading class '.$classname."\n";
            require_once
$classname.'.php';
        }
    }
}

/**
* Define function __autoload in global namespace.
*/
namespace {
   
    function
__autoload ($classname)
    {
        \
Glue\Import::load($classname);
    }

}
?>
up
2
Kavoir.com
7 months ago
For point 4, "In example, if the namespace A\B\C is imported as C" should be "In example, if the class A\B\C is imported as C".
up
0
dn dot permyakov at gmail dot com
2 months ago
Can someone explain to me -  why do we need p.4 if we have p.2 (which covers both unqualified and qualified names)?
up
-1
rangel
5 years ago
The term "autoload" mentioned here shall not be confused with __autoload function to autoload objects. Regarding the __autoload and namespaces' resolution I'd like to share the following experience:

->Say you have the following directory structure:

- root
      | - loader.php
      | - ns
             | - foo.php

->foo.php

<?php
namespace ns;
class
foo
{
    public
$say;
   
    public function
__construct()
    {
       
$this->say = "bar";
    }
   
}
?>

-> loader.php

<?php
//GLOBAL SPACE <--
function __autoload($c)
{
    require_once
$c . ".php";
}

class
foo extends ns\foo // ns\foo is loaded here
{
    public function
__construct()
    {
       
parent::__construct();
        echo
"<br />foo" . $this->say;
    }
}
$a = new ns\foo(); // ns\foo also loads ns/foo.php just fine here.
echo $a->say;   // prints bar as expected.
$b = new foo// prints foobar just fine.
?>

If you keep your directory/file matching namespace/class consistence the object __autoload works fine.
But... if you try to give loader.php a namespace you'll obviously get fatal errors.
My sample is just 1 level dir, but I've tested with a very complex and deeper structure. Hope anybody finds this useful.

Cheers!
up
-2
CJ Taylor
7 months ago
It took me playing with it a bit  as I had a hard time finding documentation on when a class name matches a namespace, if that's even legal and what behavior to expect.  It IS explained in #6 but I thought I'd share this with other souls like me that see it better by example.  Assume all 3 files below are in the same directory.

file1.php
<?php
namespace foo;

class
foo {
  static function
hello() {
    echo
"hello world!";
  }
}
?>

file2.php
<?php
namespace foo;
include(
'file1.php');

foo::hello(); //you're in the same namespace, or scope.
\foo\foo::hello(); //called on a global scope.
?>

file3.php
<?php
include('file1.php');

foo\foo::hello(); //you're outside of the namespace
\foo\foo::hello(); //called on a global scope.
?>

Depending upon what you're building (example: a module, plugin, or package on a larger application), sometimes declaring a class that matches a namespace makes sense or may even be required.  Just be aware that if you try to reference any class that shares the same namespace, omit the namespace unless you do it globally like the examples above.

I hope this is useful, particularly for those that are trying to wrap your head around this 5.3 feature.
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