Namespaces overview
(PHP 5 >= 5.3.0)
What are namespaces? In the broadest definition namespaces are a way of encapsulating items. This can be seen as an abstract concept in many places. For example, in any operating system directories serve to group related files, and act as a namespace for the files within them. As a concrete example, the file foo.txt can exist in both directory /home/greg and in /home/other, but two copies of foo.txt cannot co-exist in the same directory. In addition, to access the foo.txt file outside of the /home/greg directory, we must prepend the directory name to the file name using the directory separator to get /home/greg/foo.txt. This same principle extends to namespaces in the programming world.
In the PHP world, namespaces are designed to solve two problems that authors of libraries and applications encounter when creating re-usable code elements such as classes or functions:
- Name collisions between code you create, and internal PHP classes/functions/constants or third-party classes/functions/constants.
- Ability to alias (or shorten) Extra_Long_Names designed to alleviate the first problem, improving readability of source code.
PHP Namespaces provide a way in which to group related classes, interfaces, functions and constants. Here is an example of namespace syntax in PHP:
Example #1 Namespace syntax example
<?php
namespace my\name; // see "Defining Namespaces" section
class MyClass {}
function myfunction() {}
const MYCONST = 1;
$a = new MyClass;
$c = new \my\name\MyClass; // see "Global Space" section
$a = strlen('hi'); // see "Using namespaces: fallback to global
// function/constant" section
$d = namespace\MYCONST; // see "namespace operator and __NAMESPACE__
// constant" section
$d = __NAMESPACE__ . '\MYCONST';
echo constant($d); // see "Namespaces and dynamic language features" section
?>
Note:
Namespace names PHP and php, and compound names starting with these names (like PHP\Classes) are reserved for internal language use and should not be used in the userspace code.
- Обзор пространств имен
- Определение пространств имен
- Определение подпространств имен
- Описание нескольких пространств имен в одном файле
- Использование пространства имен: основы
- Пространства имен и динамические особенности языка
- Ключевое слово namespace и константа __NAMESPACE__
- Использование пространств имен: импорт/создание псевдонима имени
- Глобальное пространство
- Использование пространств имен: переход к глобальной функции/константе
- Правила разрешения имен
- Часто задаваемые вопросы (FAQ): вещи, которые вам необходимо знать о пространствах имен
Коментарии
Thought this might help other newbies like me...
Name collisions means:
you create a function named db_connect, and somebody elses code that you use in your file (i.e. an include) has the same function with the same name.
To get around that problem, you rename your function SteveWa_db_connect which makes your code longer and harder to read.
Now you can use namespaces to keep your function name separate from anyone else's function name, and you won't have to make extra_long_named functions to get around the name collision problem.
So a namespace is like a pointer to a file path where you can find the source of the function you are working with
Just a note: namespace (even nested or sub-namespace) cannot be just a number, it must start with a letter.
For example, lets say you want to use namespace for versioning of your packages or versioning of your API:
namespace Mynamespace\1; // Illegal
Instead use this:
namespace Mynamespace\v1; // OK
To people coming here by searching about namespaces, know that a consortium has studied about best practices in PHP, in order to allow developers to have common coding standards.
These best practices are called "PHP Standard Recommendations" , also known as PSR.
They are visible on this link : http://www.php-fig.org/psr
Actually there are 5 coding standards categories :
PSR-0 : Autoloading Standard , which goal is to make the use of Namespaces easier, in order to convert a namespace into a file path.
PSR-1 : Basic Coding Standard , basically, standards :)
PSR-2 : Coding Style Guide, where to put braces, how to write a class, etc.
PSR-3 : Logger Interface , how to write a standard logger
PSR-4 : Improved Autoloading , to resolve more Namespaces into paths.
The ones I want to point are PSR-0 and PSR-4 : they use namespaces to resolve a FQCN (Fully qualified class name = full namespace + class name) into a file path.
Basic example, you have this directory structure :
./src/Pierstoval/Tools/MyTool.php
The namespacing PSR-0 or PSR-4 standard tells that you can transform this path into a FQCN.
Read the principles of autoload if you need to know what it means, because it's almost mandatory ;) .
Structure :
{path}/autoloader.php
{path}/index.php
{path}/src/Pierstoval/Tools/MyTool.php
Files :
<?php
// {path}/index.php
include 'autoloader.php';
$tool = new Pierstoval/Tools/MyTool();
?>
<?php
// {path}/src/Pierstoval/Tools/MyTool.php
namespace Pierstoval\Tools;
class MyTool {}
?>
<?php
// {path}/autoloader.php
function loadClass($className) {
$fileName = '';
$namespace = '';
// Sets the include path as the "src" directory
$includePath = dirname(__FILE__).DIRECTORY_SEPARATOR.'src';
if (false !== ($lastNsPos = strripos($className, '\\'))) {
$namespace = substr($className, 0, $lastNsPos);
$className = substr($className, $lastNsPos + 1);
$fileName = str_replace('\\', DIRECTORY_SEPARATOR, $namespace) . DIRECTORY_SEPARATOR;
}
$fileName .= str_replace('_', DIRECTORY_SEPARATOR, $className) . '.php';
$fullFileName = $includePath . DIRECTORY_SEPARATOR . $fileName;
if (file_exists($fullFileName)) {
require $fullFileName;
} else {
echo 'Class "'.$className.'" does not exist.';
}
}
spl_autoload_register('loadClass'); // Registers the autoloader
?>
A standardized autoloader will get the class you want to instanciate (MyTool) and get the FQCN, transform it into a file path, and check if the file exists. If it does, it will <?php include(); ?> it, and if you wrote your class correctly, the class will be available within its correct namespace.
Then, if you have the following code :
<?php $tool = new Pierstoval/Tools/MyTool(); ?>
The autoloader will transform the FQCN into this path :
{path}/src/Pierstoval/Tools/MyTool.php
This might be the best practices ever in PHP framework developments, such as Symfony or others.
<?php
//Here is the simple use case of namespace. See how we can use same named class with the help of namespace. This is how namespace resolve naming collision.
namespace Mobile;
class User
{
public $name = 'mobile user';
}
$user = new \Mobile\User;
echo $user->name;
namespace TV ;
class User
{
public static $name = 'tv user';
}
echo \TV\User::$name;