You may have heard the mantra: "Code against interfaces, not implementations" or any of the popular variations thereof.

However, for people only starting out with object-oriented programming, this very abstract concept is hard to grasp initially, and it is not necessarily obvious what the actual benefit is.

I'll start by explaining the concept in abstract terms, mostly to clarify the vocabulary. Then I'll build up a practical example to show how this concept can be applied in your day-to-day WordPress PHP code. Finally, I'll go through the consequences and benefits that this way of coding will entail.