Simple DI container

Question

I'm building a web application and is trying to make my code reusable. I've decided to create components that can be used outside this project.

Now I'm trying to create a simple DI container, one class, and I would like some help checking it out. I'm thinking to do something like this:

class Container
{
 protected static $_services = array();
 protected static $_shared = array();
 /**
 * Create and store a new service in the container.
 *
 * @param string $service Service identifier name.
 * @param mixed $params Service parameters, array or a Closure object.
 * @return object Ramverk\Framework\Container.
 */
 public function add($service, $params)
 {
 if (!is_object($params) && !is_array($params)) {
 throw new Exception("Service params must be a Closure object or an array.");
 }
 static::$_services[$service] = $params;
 return $this;
 }
 /**
 * Get a shared service object, will return the same object each time.
 *
 * @param string $service Name of the shared service to get.
 * @return object Shared service object.
 */
 public function get($service)
 {
 if (!array_key_exists($service, static::$_shared)) {
 static::$_shared[$service] = $this->getNew($service);
 }
 return static::$_shared[$service];
 }
 /**
 * Get a new instance of an existing service.
 *
 * @param string $service Name of the service to create.
 * @return object Create service object.
 */
 public function getNew($service)
 {
 // Make sure service has been added
 if (!array_key_exists($service, static::$_services)) {
 throw new Exception("Service '$service' not found");
 }
 // get container service
 $container = static::$_services[$service];
 // If service is wrapped in a Closure we invoke it
 if (is_object($container)) {
 return $container();
 }
 // Make sure we have a class to work with
 if (!isset($container['class'])) {
 throw new Exception("A class must be set in $service service");
 }
 // Get service key and remove key
 $class = $container['class'];
 unset($container['class']);
 // Check if this service uses adapters
 if (array_key_exists('adapter', $container)) {
 $config = (array) $container['adapter'];
 if (!isset($config['class'])) {
 throw new Exception("An adapter class must be set in $service service");
 }
 // Grab adapter name and remove unwanted the keys
 $adapter = $config['class'];
 unset($config['class'], $container['adapter']);
 // Create the instance and return it
 return new $class(new $adapter($config));
 }
 // Create class instance and pass parameters to constructor
 return new $class($container);
 }
}

Adding a new service must contain a name (id) and either a Closure object or an array. The following will create and return the same thing:

$container = new Container();
$container->add('session', function() {
 $config = array(
 'name' => 'my_session',
 'expires' => '4 hours',
 );
 $storage = new Session\Adapter\Native($config);
 return new Session($storage);
});
// - Equals to:
$container->add('session', array(
 'class' => 'Session',
 'adapter' => array(
 'class' => 'Session\Adapter\Native',
 'name' => 'my_session',
 'expires' => '4 hours',
 ),
));
// Now I get the shared object with:
$session = $container->get('session');
// Or create a new instance
$session = $container->getNew('session');

Am I doing it right?

Answer 1

Why are you defining the properties as static? I would absolutely not do that. It means two instantiations of the Container will have the same services.

Answer 2

I think that pimple ( http://pimple-project.org/ ) is the version used in symfony 2. might be worth checking out.

• igorw: Nope, it's not used in Symfony2. It is used in Silex. And I agree with you, it's definitely a simple and good existing solution for the problem the OP is trying to solve.

Answer 3

You should read the following series of articles: http://fabien.potencier.org/article/11/what-is-dependency-injection

Additionally, the resulting component (PHP 5.2+) is there: http://components.symfony-project.org/dependency-injection/

• catalin.costache: The dependecy injection container from symfony is PHP 5.3+