Pimple

Pimple is a small Dependency Injection Container for PHP 5.3 that consists of just one file and one class (about 50 lines of code).

Download it, require it in your code, and you're good to go:

require_once '/path/to/Pimple.php';

Creating a container is a matter of instating the Pimple class:

$container = new Pimple();

As many other dependency injection containers, Pimple is able to manage two different kind of data: objects and parameters.

Defining Parameters

Defining a parameter is as simple as using the Pimple instance as an array:

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

Defining Objects

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

// define some objects
$container['session_storage'] = function ($c) {
    return new $c['session_storage_class']($c['cookie_name']);
};

$container['session'] = function ($c) {
    return new Session($c['session_storage']);
};

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

As objects are only created when you get them, the order of the definitions does not matter, and there is no performance penalty.

Using the defined objects 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 Shared Objects

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

$c['session'] = $c->share(function ($c) {
    return new Session($c['session_storage']);
});

Protecting Parameters

As Pimple makes no difference between a parameter and an object, you can use the protect() method if you need to define a parameter as an anonymous function:

$c['random'] = $c->protect(function () { return rand(); });

When you want to set the the value of a parameter to an existing (global) function name, you must also protect it. For example:

$container['log_function'] = $container->protect('var_dump');

Packaging a Container for reusability

If you use the same libraries over and over, you might want to create reusable containers. Creating a reusable container is as simple as creating a class that extends Pimple, and configuring it in the constructor:

class SomeContainer extends Pimple
{
    public function __construct()
    {
        $this['parameter'] = 'foo';
        $this['object'] = function () { return stdClass(); };
    }
}

Using this container from your own is as easy as it can get: