On Scotch.io today they've posted a tutorial about SOLID, the "first five principles of object oriented design". SOLID is an acronym made from the first letter of several principles that can help make your OOP code well-architected and easier to test.

S.O.L.I.D is an acronym for the first five object-oriented design(OOD) principles by Robert C. Martin, popularly known as Uncle Bob. These principles, when combined together, make it easy for a programmer to develop software that are easy to maintain and extend. They also make it easy for developers to avoid code smells, easily refactor code, and are also a part of the agile or adaptive software development. Note: this is just a simple “welcome to S.O.L.I.D” article, it simply sheds light on what S.O.L.I.D is.

They start with a basic overview of what the letters in SOLID stand for and then work through each, providing basic code examples to help make the point clearer.