Pimple

Pimple is a small Dependency Injection Container for PHP.

Installation

Before using Pimple in your project, add it to your composer.json file:

$ ./composer.phar require pimple/pimple "^3.0"

Usage

Creating a container is a matter of creating a Container instance:

use Pimple\Container;

$container = new Container();

As many other dependency injection containers, Pimple manages two different kind of data: services and parameters.

Defining Services

A service is an object that does something as part of a larger system. Examples of services: a database connection, a templating engine, or a mailer. Almost any global object can be a service.

Services are defined by anonymous functions that return an instance of an object:

// define some services
$container['session_storage'] = fn($c) => new SessionStorage('SESSION_ID');

$container['session'] = fn($c) => new Session($c['session_storage']);

Notice that the anonymous function has access to the current container instance, allowing references to other services or parameters.

As objects are only created when you get them, the order of the definitions does not matter.

Using the defined services is also very easy:

// get the session object
$session = $container['session'];

// the above call is roughly equivalent to the following code:
// $storage = new SessionStorage('SESSION_ID');
// $session = new Session($storage);

Defining Factory Services

By default, each time you get a service, Pimple returns the same instance of it. If you want a different instance to be returned for all calls, wrap your anonymous function with the factory() method

$container['session'] = $container->factory(fn($c) => new Session($c['session_storage']));

Now, each call to $container['session'] returns a new instance of the session.

Defining Parameters

Defining a parameter allows to ease the configuration of your container from the outside and to store global values:

// define some parameters
$container['cookie_name'] = 'SESSION_ID';
$container['session_storage_class'] = 'SessionStorage';

If you change the session_storage service definition like below:

$container['session_storage'] = fn($c) => new $c['session_storage_class']($c['cookie_name']);

You can now easily change the cookie name by overriding the cookie_name parameter instead of redefining the service definition.

Protecting Parameters

Because Pimple sees anonymous functions as service definitions, you need to wrap anonymous functions with the protect() method to store them as parameters:

$container['random_func'] = $container->protect(fn() => rand());

Modifying Services after Definition

In some cases you may want to modify a service definition after it has been defined. You can use the extend() method to define additional code to be run on your service just after it is created:

$container['session_storage'] = fn($c) => new $c['session_storage_class']($c['cookie_name']);

$container->extend('session_storage', function ($storage, $c) {
    $storage->...();

    return $storage;
});

The first argument is the name of the service to extend, the second a function that gets access to the object instance and the container.

Extending a Container

If you use the same libraries over and over, you might want to reuse some services from one project to the next one; package your services into a provider by implementing Pimple\ServiceProviderInterface:

use Pimple\Container;

class FooProvider implements Pimple\ServiceProviderInterface
{
    public function register(Container $pimple)
    {
        // register some services and parameters
        // on $pimple
    }
}

Then, register the provider on a Container:

$pimple->register(new FooProvider());

Fetching the Service Creation Function

When you access an object, Pimple automatically calls the anonymous function that you defined, which creates the service object for you. If you want to get raw access to this function, you can use the raw() method:

$container['session'] = fn($c) => new Session($c['session_storage']);

$sessionFunction = $container->raw('session');

PSR-11 compatibility

For historical reasons, the Container class does not implement the PSR-11 ContainerInterface. However, Pimple provides a helper class that will let you decouple your code from the Pimple container class.

The PSR-11 container class

The Pimple\Psr11\Container class lets you access the content of an underlying Pimple container using Psr\Container\ContainerInterface methods:

use Pimple\Container;
use Pimple\Psr11\Container as PsrContainer;

$container = new Container();
$container['service'] = fn($c) => new Service();
$psr11 = new PsrContainer($container);

$controller = function (PsrContainer $container) {
    $service = $container->get('service');
};
$controller($psr11);

Using the PSR-11 ServiceLocator

Sometimes, a service needs access to several other services without being sure that all of them will actually be used. In those cases, you may want the instantiation of the services to be lazy.

The traditional solution is to inject the entire service container to get only the services really needed. However, this is not recommended because it gives services a too broad access to the rest of the application and it hides their actual dependencies.

The ServiceLocator is intended to solve this problem by giving access to a set of predefined services while instantiating them only when actually needed.

It also allows you to make your services available under a different name than the one used to register them. For instance, you may want to use an object that expects an instance of EventDispatcherInterface to be available under the name event_dispatcher while your event dispatcher has been registered under the name dispatcher:

use Monolog\Logger;
use Pimple\Psr11\ServiceLocator;
use Psr\Container\ContainerInterface;
use Symfony\Component\EventDispatcher\EventDispatcher;

class MyService
{
    /**
     * "logger" must be an instance of Psr\Log\LoggerInterface
     * "event_dispatcher" must be an instance of Symfony\Component\EventDispatcher\EventDispatcherInterface
     */
    private $services;

    public function __construct(ContainerInterface $services)
    {
        $this->services = $services;
    }
}

$container['logger'] = fn($c) => new Monolog\Logger();
$container['dispatcher'] = fn($c) => new EventDispatcher();

$container['service'] = function ($c) {
    $locator = new ServiceLocator($c, array('logger', 'event_dispatcher' => 'dispatcher'));

    return new MyService($locator);
};

Referencing a Collection of Services Lazily

Passing a collection of services instances in an array may prove inefficient if the class that consumes the collection only needs to iterate over it at a later stage, when one of its method is called. It can also lead to problems if there is a circular dependency between one of the services stored in the collection and the class that consumes it.

The ServiceIterator class helps you solve these issues. It receives a list of service names during instantiation and will retrieve the services when iterated over:

use Pimple\Container;
use Pimple\ServiceIterator;

class AuthorizationService
{
    private $voters;

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

    public function canAccess($resource)
    {
        foreach ($this->voters as $voter) {
            if (true === $voter->canAccess($resource)) {
                return true;
            }
        }

        return false;
    }
}

$container = new Container();

$container['voter1'] = fn($c) => new SomeVoter();
$container['voter2'] = fn($c) => new SomeOtherVoter($c['auth']);
$container['auth'] = fn ($c) => new AuthorizationService(new ServiceIterator($c, array('voter1', 'voter2'));