PHP: Espacios de nombres y características dinámicas del lenguaje

Espacios de nombres y características dinámicas del lenguaje

(PHP 5 >= 5.3.0, PHP 7, PHP 8)

La implementación de PHP de los espacios de nombres está influenciada por su naturaleza dinámica como lenguaje de programación. Así, para convertir código como el del siguiente ejemplo en código de espacios de nombres:

Ejemplo #1 Acceder dinámicamente a elementos

ejemplo1.php:

<?php
class nombre_clase
{
    function __construct()
    {
        echo __METHOD__,"\n";
    }
}
function nombre_func()
{
    echo __FUNCTION__,"\n";
}
const nombre_const = "global";

$a = 'nombre_clase';
$obj = new $a; // imprime nombre_clase::__construct
$b = 'nombre_func';
$b(); // imprime nombre_func
echo constant('nombre_const'), "\n"; // imprime global
?>

se debe emplear el nombre completamente cualificado (nombre de clase con prefijo de espacio de nombres). Observe que, debido a que no hay diferencia entre un nombre cualificado y uno completamente cualificado dentro de un nombre de clase, función, o constante dinámicas, no es necesario la barra invertida inicial.

Ejemplo #2 Acceder dinámicamente a elementos de un espacio de nombres

<?php
namespace nombre_espacio_de_nombres;
class nombre_clase
{
    function __construct()
    {
        echo __METHOD__,"\n";
    }
}
function nombre_func()
{
    echo __FUNCTION__,"\n";
}
const nombre_const = "de espacio de nombres";

/* observe que si se emplean comillas dobles, se debe usar "\\nombre_espacio_de_nombres\\nombre_clase" */
$a = '\nombre_espacio_de_nombres\nombre_clase';
$obj = new $a; // imprime nombre_espacio_de_nombres\nombre_clase::__construct
$a = 'nombre_espacio_de_nombres\nombre_clase';
$obj = new $a; // también imprime nombre_espacio_de_nombres\nombre_clase::__construct
$b = 'nombre_espacio_de_nombres\nombre_func';
$b(); // imprime nombre_espacio_de_nombres\nombre_func
$b = '\nombre_espacio_de_nombres\nombre_func';
$b(); // también imprime nombre_espacio_de_nombres\nombre_func
echo constant('\nombre_espacio_de_nombres\nombre_const'), "\n"; // imprime de espacio de nombres
echo constant('nombre_espacio_de_nombres\nombre_const'), "\n"; // también imprime de espacio de nombres
?>

Asegúrese de leer la nota sobre escapar nombres de espacios de nombres en cadenas.

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User Contributed Notes 8 notes

down

Alexander Kirk ¶

13 years ago

When extending a class from another namespace that should instantiate a class from within the current namespace, you need to pass on the namespace.

<?php // File1.php
namespace foo;
class A {
    public function factory() {
        return new C;
    }
}
class C {
    public function tell() {
        echo "foo";
    }
}
?>

<?php // File2.php
namespace bar;
class B extends \foo\A {}
class C {
    public function tell() {
        echo "bar";
    }
}
?>

<?php
include "File1.php";
include "File2.php";
$b = new bar\B;
$c = $b->factory();
$c->tell(); // "foo" but you want "bar"
?>

You need to do it like this:

When extending a class from another namespace that should instantiate a class from within the current namespace, you need to pass on the namespace.

<?php // File1.php
namespace foo;
class A {
    protected $namespace = __NAMESPACE__;
    public function factory() {
        $c = $this->namespace . '\C';
        return new $c;
    }
}
class C {
    public function tell() {
        echo "foo";
    }
}
?>

<?php // File2.php
namespace bar;
class B extends \foo\A {
    protected $namespace = __NAMESPACE__;
}
class C {
    public function tell() {
        echo "bar";
    }
}
?>

<?php
include "File1.php";
include "File2.php";
$b = new bar\B;
$c = $b->factory();
$c->tell(); // "bar"
?>

(it seems that the namespace-backslashes are stripped from the source code in the preview, maybe it works in the main view. If not: fooA was written as \foo\A and barB as bar\B)

down

Daan ¶

5 years ago

Important to know is that you need to use the *fully qualified name* in a dynamic class name. Here is an example that emphasizes the difference between a dynamic class name and a normal class name.

<?php
namespace namespacename\foo;

class classname      
{                                                                                        
    function __construct()                                                               
    {                                                                                    
        echo 'bar';
    }                                                                                    
}                                                                                        

$a = '\namespacename\foo\classname'; // Works, is fully qualified name                   
$b = 'namespacename\foo\classname'; // Works, is treated as it was with a prefixed "\"   
$c = 'foo\classname'; // Will not work, it should be the fully qualified name            

// Use dynamic class name                                                                                         
new $a; // bar
new $b; // bar
new $c; // [500]: / - Uncaught Error: Class 'foo\classname' not found in 

// Use normal class name                                                                                         
new \namespacename\foo\classname; // bar
new namespacename\foo\classname; // [500]: / - Uncaught Error: Class 'namespacename\foo\namespacename\foo\classname' not found
new foo\classname; // [500]: / - Uncaught Error: Class 'namespacename\foo\foo\classname' not found

down

museyib dot e at gmail dot com ¶

5 years ago

Be careful when using dynamic accessing namespaced elements. If you use double-quote backslashes will be parsed as escape character.

<?php
    $a="\namespacename\classname"; //Invalid use and Fatal error.
    $a="\\namespacename\\classname"; //Valid use.
    $a='\namespacename\classname'; //Valid use.
?>

down

guilhermeblanco at php dot net ¶

15 years ago

Please be aware of FQCN (Full Qualified Class Name) point.

Many people will have troubles with this:



<?php



// File1.php

namespace foo;



class Bar { ... }



function factory($class) {

    return new $class;

}



// File2.php

$bar = \foo\factory('Bar'); // Will try to instantiate \Bar, not \foo\Bar



?>



To fix that, and also incorporate a 2 step namespace resolution, you can check for \ as first char of $class, and if not present, build manually the FQCN:



<?php



// File1.php

namespace foo;



function factory($class) {

    if ($class[0] != '\\') {

        echo '->';

         $class = '\\' . __NAMESPACE__ . '\\' . $class;

    }



    return new $class();

}



// File2.php

$bar = \foo\factory('Bar'); // Will correctly instantiate \foo\Bar



$bar2 = \foo\factory('\anotherfoo\Bar'); // Wil correctly instantiate \anotherfoo\Bar



?>

down

akhoondi+php at gmail dot com ¶

11 years ago

It might make it more clear if said this way: 

One must note that when using a dynamic class name, function name or constant name, the "current namespace", as in http://www.php.net/manual/en/language.namespaces.basics.php is global namespace.

One situation that dynamic class names are used is in 'factory' pattern. Thus, add the desired namespace of your target class before the variable name.

namespaced.php
<?php
// namespaced.php
namespace Mypackage;
class Foo {
    public function factory($name, $global = FALSE)
    {
        if ($global)
            $class = $name;
        else
            $class = 'Mypackage\\' . $name;
        return new $class;
    }
}

class A {
    function __construct()
    {
        echo __METHOD__ . "<br />\n";
    }
}
class B {
    function __construct()
    {
        echo __METHOD__ . "<br />\n";
    }
}
?>

global.php
<?php 
// global.php
class A {
    function __construct()
    {
        echo  __METHOD__;
    }
}
?>

index.php
<?php
//  index.php
namespace Mypackage;
include('namespaced.php');
include('global.php');
  
  $foo = new Foo();
  
  $a = $foo->factory('A');        // Mypackage\A::__construct 
  $b = $foo->factory('B');        // Mypackage\B::__construct
  
  $a2 = $foo->factory('A',TRUE);    // A::__construct
  $b2 = $foo->factory('B',TRUE);    // Will produce : Fatal error: Class 'B' not found in ...namespaced.php on line ...
?>

down

m dot mannes at gmail dot com ¶

7 years ago

Case you are trying call a static method that's the way to go:

<?php
class myClass 
{
    public static function myMethod() 
    {
      return "You did it!\n";
    }
}

$foo = "myClass";
$bar = "myMethod";

echo $foo::$bar(); // prints "You did it!";
?>

down

anisgazig at gmail dot com ¶

3 years ago

<?php

//single or double quotes with single or double backslash in dynamic namespace class.

namespace Country_Name{
class Mexico{
function __construct(){
echo __METHOD__,"<br>";
}
}

$a = 'Country_Name\Mexico';//Country_Name\Mexico::__construct
$a = "Country_Name\Mexico";
//Country_Name\Mexico::__construct
$a = '\Country_Name\Mexico';
//Country_Name\Mexico::__construct
$a = "\Country_Name\Mexico";
//Country_Name\Mexico::__construct
$a = "\\Country_Name\\Mexico";
//Country_Name\Mexico::__construct
$o = new $a;

}

/* if your namespace name or class name start with lowercase n then you should be alart about the use of single or double quotes with backslash  */

namespace name_of_country{
class Japan{
function __construct()
{
    echo __METHOD__,"<br>";
}

}

$a = 'name_of_country\Japan';
//name_of_country\Japan::__construct
$a = "name_of_country\Japan";
//name_of_country\Japan::__construct
$a = '\name_of_country\Japan';
//name_of_country\Japan::__construct
//$a = "\name_of_country\Japan";
//Fatal error: Uncaught Error: Class ' ame_of_country\Japan' not found 
//In this statement "\name_of_country\Japan" means -first letter n with "\ == new line("\n). for fix it we can use double back slash or single quotes with single backslash. 
$a = "\\name_of_country\\Japan";
//name_of_country\Japan::__construct
$o = new $a;
}

namespace Country_Name{
class name{
function __construct(){
echo __METHOD__,"<br>";
}
}

$a = 'Country_Name\name';
//Country_Name\Norway::__construct
$a = "Country_Name\name";
//Country_Name\Norway::__construct
$a = '\Country_Name\name';
//Country_Name\Norway::__construct
//$a = "\Country_Name\name";
//Fatal error: Uncaught Error: Class '\Country_Name ame' not found 

//In this statement "\Country_Name\name" at class name's first letter n with "\ == new line("\n). for fix it we can use double back slash or single quotes with single backslash
$a = "\\Country_Name\\name";
//Country_Name\name::__construct
$o = new $a;

}

//"\n == new line are case insensitive so "\N could not affected

 ?>

down

scott at intothewild dot ca ¶

15 years ago

as noted by guilhermeblanco at php dot net, 

<?php

  // fact.php

  namespace foo;

  class fact {

    public function create($class) {
      return new $class();
    }
  }

?>

<?php 

  // bar.php

  namespace foo;

  class bar {
  ... 
  }

?>

<?php

  // index.php
 
  namespace foo;

  include('fact.php');
  
  $foofact = new fact();
  $bar = $foofact->create('bar'); // attempts to create \bar
                                  // even though foofact and
                                  // bar reside in \foo

?>

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