set() public method
Registers a class definition with this container. For example, // register a class name as is. This can be skipped.
$container->set('yii\db\Connection');
// register an interface
// When a class depends on the interface, the corresponding class
// will be instantiated as the dependent object
$container->set('yii\mail\MailInterface', 'yii\swiftmailer\Mailer');
// register an alias name. You can use $container->get('foo')
// to create an instance of Connection
$