Definir espacios de nombres

(PHP 5 >= 5.3.0)

Aunque cualquier código de PHP válido puede estar contenido dentro de un espacio de nombres, solamente se ven afectados por espacios de nombres los siguientes tipos de código: clases (incluyendo abstractas y traits), interfaces, funciones y constantes.

Los espacios de nombres se declaran usando la palabra clave namespace. Un archivo que contiene un espacio de nombres debe declararlo al inicio del archivo, antes que cualquier otro código - con una excepción: la palabra clave declare.

Ejemplo #1 Declarar un único espacio de nombres

<?php
namespace MiProyecto;

const 
CONECTAR_OK 1;
class 
Conexión /* ... */ }
function 
conectar() { /* ... */  }

?>
La única construcción de código permitida antes de la declaración de un espacio de nombres es la sentencia declare, para declarar la codificación de un archivo fuente. Además, algo que no sea código de PHP no puede preceder a la declaración del espacio de nombres, incluyendo espacios en blanco extra:

Ejemplo #2 Declarar un único espacio de nombres

<html>
<?php
namespace MiProyecto// error fatal - el espacio de nombres debe ser la primera sentencia del script
?>

Además, a diferencia de otras construcciones de PHP, se puede definir el mismo espacio de nombres en múltiples archivos, permitiendo la separación de contenido de espacios de nombres a través del sistema de archivos.

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User Contributed Notes 9 notes

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26
danbettles at yahoo dot co dot uk
5 years ago
Regarding constants defined with define() inside namespaces...

define() will define constants exactly as specified.  So, if you want to define a constant in a namespace, you will need to specify the namespace in your call to define(), even if you're calling define() from within a namespace.  The following examples will make it clear.

The following code will define the constant "MESSAGE" in the global namespace (i.e. "\MESSAGE").

<?php
namespace test;
define('MESSAGE', 'Hello world!');
?>

The following code will define two constants in the "test" namespace.

<?php
namespace test;
define('test\HELLO', 'Hello world!');
define(__NAMESPACE__ . '\GOODBYE', 'Goodbye cruel world!');
?>
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11
jeremeamia at gmail dot com
4 years ago
You should not try to create namespaces that use PHP keywords. These will cause parse errors.

Examples:

<?php
namespace Project/Classes/Function; // Causes parse errors
namespace Project/Abstract/Factory; // Causes parse errors
?>
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8
FatBat
8 months ago
Expanding on @danbettles note, it is better to always be explicit about which constant to use.

<?php
   
namespace NS;

   
define(__NAMESPACE__ .'\foo','111');
   
define('foo','222');

    echo
foo// 111.
   
echo \foo// 222.
   
echo \NS\foo  // 111.
   
echo NS\foo  // fatal error. assumes \NS\NS\foo.
?>
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11
huskyr at gmail dot com
4 years ago
"A file containing a namespace must declare the namespace at the top of the file before any other code"

It might be obvious, but this means that you *can* include comments and white spaces before the namespace keyword.

<?php
// Lots
// of
// interesting
// comments and white space

namespace Foo;
class
Bar {
}
?>
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5
Baptiste
5 years ago
There is nothing wrong with PHP namespaces, except that those 2 instructions give a false impression of package management.
... while they just correspond to the "with()" instruction of Javascript.

By contrast, a package is a namespace for its members, but it offers more (like deployment facilities), and a compiler knows exactly what classes are in a package, and where to find them.
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3
Anonymous
6 years ago
@ RS: Also, you can specify how your __autoload() function looks for the files. That way another users namespace classes cannot overwrite yours unless they replace your file specifically.
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4
David Drakard
5 years ago
I agree with SR, the new namespaces feature has solved a number of problems for me which would have required horrible coding to solve otherwise.

An example use:
Say you are making a small script, and write a class to connect to a database, calling it 'connection'. If you find your script useful and gradually expand it into a large application, you may want to rename the class. Without namespaces, you have to change the name and every reference to it (say in inheriting objects), possibly creating a load of bugs. With namespaces you can drop the related classes into a namespace with one line of code, and less chance of errors.

This is by no means one of the biggest problems namespaces solve; I would suggest reading about their advantages before citicising them. They provide an elegant solutions to several problems involved in creating complex systems.
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-2
Roadowl
1 month ago
quote:
Defining namespaces

(...)
Namespaces are declared using the namespace keyword. A file containing a namespace must declare the namespace at the top of the file before any other code - with one exception: the declare keyword.

end quote.

So we have a title that talks 'defining' and a piece of text that talks 'declare' three times, one of which could be referring to some other 'declare' than the former two.

Please, documentation authors -- get your act together, finally.
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-11
wyattbiker
10 months ago
<?php
//Even though you cant add anything before the 1st namespace, you can add something before subsequent namespaces.
namespace MyProject;

function
myfunc(){
    return
1;
}
echo
myfunc();
?>
<p>Here I can add stuff before the 2nd namespace</p>
<?php

namespace MyProject2;

function
myfunc(){
    return
2;
}
echo
myfunc();
?>
<p>Switch back to first namespace</p>
<?php
namespace MyProject;
echo
myfunc();
?>
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