Carl Alexander’s Free Guide to Object-Oriented Programming in WordPress
Carl Alexander is a great technical writer, and he’s doing a great service for the world of WordPress: He teaches the principles of object-oriented programming (OOP).
His content is very rich, well-written, and currently free, so if you’ve been wanting to learn object-oriented programming, how it applies to WordPress, and how to learn to think in OOP coming from a WordPress development background, he should be your first stop. And for your first stop’s first stop, I’d recommend getting his free course introducing the fundamentals. Just browsing the site is very valuable too—start at his Library page and see what catches your eye.