Introduction¶

ExpressionEngine’s core is built around a dependency container:

use EllisLab\ExpressionEngine\Service\Dependency\InjectionContainer;
$di = new InjectionContainer();

This is simply a container of named objects or factories. The container itself is not public. Additions are made by declaring them in the addon.setup file.

Retrieving Data¶

Anything stored on a dependency container can be retrieve with make():

$di->make('Something');

This method is exposed globally as ee():

ee('Something');

Adding Objects¶

You can add objects directly to a dependency container and then call make() to retrieve them:

$di->register('Member', $member);

$di->make('Member') == $member // true

Creating Factories¶

If a closure is added to the dependency container, it will be treated as a factory:

$di->register('User', function($di, $name)
{
  return new User($name);
});

When you make() an item that is a closure, it will be executed and its result will be returned. The first parameter to the closure will always be the dependency object that holds it. All other parameters will be any additional ones that were passed to make():

$u1 = $di->make('User', 'Bob');
$u2 = $di->make('User', 'Bob');
$u3 = $di->make('User', 'Alice');

// $u1 != $u2 != $u3

Hiding Dependencies¶

The first parameter to a closure inside a dependency container is always the container itself. This means you can nest calls to the container to resolve complex dependencies without exposing them in your public API:

$di->register('Database', function($di, $name)
{
  return new Database($name);
})

$di->register('Session', function($di)
{
  return new Session(
    $di->make('Database', 'local')
  );
});

$di->make('Session'); // no mention of a database