Level: advance
An example of how can you extend an existing service .
php app.php
I defined a service 'OPERATIONS' inside the CalculatorDependencyProvider. That is an array of multiple "operations"
that will be processed later in the Calculator class - following an example of a stack-plugin pattern.
This examples shows how easy you can extend any service before it's used. This can be really helpful if you want to allow your app to be extended by other usages/apps without the need of inheritance in your codebase when they need extra functionality.