ProjectExtension.php

<?php

use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\DependencyInjection\Definition;
use Symfony\Component\DependencyInjection\Extension\ExtensionInterface;
class ProjectExtension implements ExtensionInterface {
  public function load(array $configs, ContainerBuilder $configuration) {
    $config = call_user_func_array('array_merge', $configs);
    $configuration
      ->setDefinition('project.service.bar', new Definition('FooClass'));
    $configuration
      ->setParameter('project.parameter.bar', isset($config['foo']) ? $config['foo'] : 'foobar');
    $configuration
      ->setDefinition('project.service.foo', new Definition('FooClass'));
    $configuration
      ->setParameter('project.parameter.foo', isset($config['foo']) ? $config['foo'] : 'foobar');
    return $configuration;
  }
  public function getXsdValidationBasePath() {
    return false;
  }
  public function getNamespace() {
    return 'http://www.example.com/schema/project';
  }
  public function getAlias() {
    return 'project';
  }
  public function getConfiguration(array $config, ContainerBuilder $container) {
    return null;
  }

}