src/Application.php
protected function initializeContainer()
    {
        $this->registerDefaultExtensions();
        $initializer = $this->getContainerInitializer();
        $this->container = $initializer->initializeContainer($this, $this->extensions, $this->compilerPasses);
        $this->container->set('app', $this);

        return $this->container;
    }
protected function initializeContainer()
    {
        $this->registerDefaultExtensions();
        $initializer = $this->getContainerInitializer();
        $this->container = $initializer->initializeContainer($this, $this->extensions, $this->compilerPasses);
        $this->container->set('app', $this);

        return $this->container;
    }
Initializes a new container.

@return ContainerInterface