Namespaces serve as qualifiers that enhance organization by grouping related classes that collaborate to accomplish a task. They also allow multiple classes to share the same name without conflicts.
For instance, consider a group of classes representing a car, such as Car, Engine, and Wheel, and another group representing a train, like Length, Engine, and Track. By using namespaces, you can organize these classes into separate groups, ensuring that identical class names, such as Engine, are distinguished and don’t conflict.
Declaring a Namespace
Syntax: Namespaces are defined at the start of a PHP file using the namespace keyword. This is must.
Example:
<?php
namespace Vehicle;
echo "Welcome to WebmasterMaze";
...
?>Using Namespaces
Constants, classes, and functions defined in the namespace file become a part of that namespace.
Any code that follows a namespace declaration operates within that namespace, allowing classes to be instantiated without any additional qualifiers.
Example:
<?php
namespace Vehicle;
?>
<!DOCTYPE html>
<html>
<body>
<?php
// Defining a class within the Vehicle namespace
class Car {
public $make;
public $model;
public function __construct($make, $model) {
$this->make = $make;
$this->model = $model;
}
}
// Defining a constant
const VEHICLE_TYPE = 'Car';
// Defining a function
function getVehicleType() {
return VEHICLE_TYPE;
}
$myCar = new Car('Toyota', 'Corolla'); // Create an instance of the Car class
echo $myCar->make . "<br>"; // Output: Toyota
echo $myCar->model . "<br>"; // Output: Corolla
echo getVehicleType(); // Output: Car
echo "<br>"; // New line for clarity
// Output the constant value
echo VEHICLE_TYPE; // Output: Car
?>
</body>
</html>To access classes from outside the namespace, the namespace must be prefixed to the class.
Example: Suppose if a vehicle namespace has two classes Car and Bike, then the code to utilize those classes will be:
$car = new Vehicle\Car();
$bike = new Vehicle\Bike();When multiple classes from the same namespace are used simultaneously, it is more convenient to use the namespace keyword, as shown below:
<?php
namespace Vehicle;
$car = new Car(); // No need to use Vehicle\
$bike = new Bike();
?>Nested Namespaces
For better organization, nested namespaces can be used.
Example: Declare a namespace named Vehicle within a namespace called Transport.
<?php
namespace Transport\Vehicle;
?>Namespace Alias
Giving a namespace or class an alias can simplify code writing. This can be achieved using the use keyword.
Example:
<?php
// Use aliasing for Vehicle\Car and Vehicle\Bike
use Vehicle\Car as C;
use Vehicle\Bike as B;
// Create instances using the aliases
$car = new C("Toyota", "Corolla");
$bike = new B("Honda", "CBR");
?>