To implement a central storage for objects often used throughout the application, is typically implemented using an abstract class with only static methods (or using the Singleton pattern). Remember that this introduces global state, which should be avoided at all times! Instead implement it using Dependency Injection!
You can also find this code on GitHub
Registry.php
Registry.php
Service.php
Service.php
Tests/RegistryTest.php
Tests/RegistryTest.php