What is namespace in PHP and it's use?

What is a Namespace?

A namespace is a way to group related classes, functions, and constants together, avoiding conflicts with other code.

Defining a Namespace

A namespace is defined using the namespace keyword followed by the namespace name.

namespace Core;

Using the use Keyword

The use keyword is used to import classes, functions, and constants from other namespaces into the current namespace.

use PDO;

This imports the PDO class from the global namespace into the current namespace (Core).

namespace Core;
use PDO;

class Database {
    public $connection;
    public $statement;

    public function __construct($config, $username = 'root', $password = '') {
        $dsn = 'mysql:' . http_build_query($config, '', ';');
        $this->connection = new PDO($dsn, $username, $password, [
            PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC
        ]);
    }
}

Without the use Keyword

Without the use keyword, you would have to use the fully qualified name of the PDO class, like this \PDO:

namespace Core;

class Database {
    public $connection;
    public $statement;

    public function __construct($config, $username = 'root', $password = '') {
        $dsn = 'mysql:' . http_build_query($config, '', ';');
        $this->connection = new \PDO($dsn, $username, $password, [
            \PDO::ATTR_DEFAULT_FETCH_MODE => \PDO::FETCH_ASSOC
        ]);
    }
}

Importing Namespaces

Namespaces can be imported using the use keyword, like this:

use Core\Database;

This imports the Database class from the Core namespace into the current namespace.

When to Use Namespaces

Namespaces are useful when:

• You want to avoid conflicts with other code.
• You want to organize your code into logical groups.
• You want to use classes, functions, and constants from other namespaces.

use Core\Database;

$db = new Database($config['database']);

Autoloading Classes and Functions

You can automatically load classes and functions using the spl_autoload_register function. But first, you need to change the autoloader statement of last project spl_autoload_register(function ($class) { require base_path("Core/{$class}.php"); });

to this:

spl_autoload_register(function ($class) { 
    $class = str_replace('\\', DIRECTORY_SEPARATOR, $class); 
    require base_path("{$class}.php"); 
});

The statement str_replace('\\', DIRECTORY_SEPARATOR, $class); tells that:

• str_replace is a PHP function that replaces a string with another string.
• The first argument ('\\', is the string to be replaced, which is the namespace separator (\).
• The second argument DIRECTORY_SEPARATOR is the string that will replace the namespace separator. DIRECTORY_SEPARATOR is a PHP constant that represents the directory separator (either / or \, depending on the operating system).
• The third argument $class is the string that contains the class name, which may include namespace separators (\).

I hope that you have clearly understood it.

Comments

[david duymelinck]

A great article!

I would added a section about composer, because that is the way autoloading is done in an organised way.

An example of loading classes and functions

{
     "autoload": {
        "psr-4": {"Acme\\": "src/"}
       "files": ["src/helpers.php"]
    }
}

With the psr-4 key all classes in the src folder will be autoladed with Acme as the vendor namespace.
With the files key you can add files that only contain functions.

[Zubair Mohsin]

Good work!