PHP Dependency Injection

Keyword: PHP-DI, PSR-11, Autowriing

Dependency injection allow you inject an object into another object¹.

Dependency Injection Container is the way to manage injecting and reading objects and third party libraries in your application.

PHP-FIG PSR-11² is a standard guide you to implement container.

interface ContainerInterface {
    public function get($id);
    public function has($id);
}

Example

class Wheel
{

}

class Car
{
    private $wheel;

    public function __construct(Wheel $wheel)
   {
      $this->wheel = $wheel;
   }
}


$wheel = new Wheel;

$car = new Car($wheel);

At above example, every new Car object need Wheel object. That is dependency. new Car object is dependent on Wheel object.

As we can see, PSR-11 define two method has and get. get method will resolve dependency by using Reflection³. It provides autowiring⁴.

PHP has native Reflection⁵.

Want study more about dependency injection, check out PHP-DI⁶.

There is also another example demo a very simple container⁷.