Dependency injection¶

Dependency Injection is a process by which the components a class uses are supplied to it by a container instead of the class itself locating them. This allows a ton of flexibility for testing, special cases, and polymorhpism, and it follows the "tell, don't ask" software design principle.

The Xyster team has implemented a Dependency Injection container. Here's an example of how you might use the container. (This example is adapted from one listed on the PicoContainer site).

 interface Peelable {  
     function peel();  
 }  
 class Apple implements Peelable {  
     public function peel()
     {  
     }  
 }
 class Peeler {  
     private $_peelable;  
     public function __construct(Peelable $peelable)
     {  
         $this->_peelable = $peelable;  
     }  
 }
 class Juicer {  
     private $_peelable;  
     private $_peeler;  
     public function __construct(Peelable $peelable, Peeler $peeler)
     {  
         $this->_peelable = $peelable;  
         $this->_peeler = $peeler;  
     }  
 }

Add components:

 $container = new Xyster_Container;
 $container->addComponent("Apple");
 $container->addComponent("Juicer");
 $container->addComponent("Peeler");

Get component with dependencies injected:

 $juicer = $container->getComponent("Juicer");

If you're curious about the implementation and would like to test it out before it's stable, have a look at Xyster_Container in the incubator.