Services and the dependency injection container

Another architecturally important element of Drupal 8 is the Symfony dependency injection component (http://symfony.com/doc/current/components/dependency_injection.html), specifically represented by the service container.

This component is a staple of modern OOP PHP programming and as such has become foundational to Drupal 8. It allows us to create services that can be injected in various places of our code in order to handle certain functional (and oftentimes swappable) tasks. Additionally, they can also be used as an extension point because the service container is able to group services that have very specific responsibilities and use them for that automatically. In other words, simply by defining a simple service, we can provide our own functionality or even change existing logic.

We will encounter many services, and we will see how we can declare our own later in this book.