These days, it's hard to appreciate that Object-Oriented Programming is so easy, it was taught to kids in junior high before it was ever taught to adults. As supposedly senior software engineers debate whether a Car truly "is a" Vehicle, and whether it wouldn't be easier to learn lambda calculus and determine the median monad blog post than to reflect the real objects in the real-world problem they're solving in their software, it seems reasonable to ask: is it really so difficult?

From October 24th to 29th, 1927, twenty-nine scientists gathered in Brussels for the fifth Solvay Conference. Among the attendees, of which seventeen got a Nobel Prize before or after attending, were Erwin Schrödinger, Wolfgang Pauli, Werner Heisenberg, Paul Dirac, Louis de Broglie, Max Born, Niels Bohr, Max Planck, Marie Curie, Hendrik Lorentz, and Albert Einstein. One might think there might have not been such an assembly of brilliant thinkers since the Platonic Academy.

Many developers will have heard of Barbara Liskov, through her appearance in Robert C. Martin's SOLID list of design principles. The abstract of her 1994 paper with Jeanette Wing, A Behavioral Notion of Subtyping, makes the principle sound easy in, well, in principle.

When the author of these words started its career as a software developer, "object orientation" was all the rage. "Serious" programming languages were object oriented. "Professional" programming environments allowed one to view "objects" and "classes" in all of their glory. Inheritance, not composition, was the way of the future. Design patterns names were the answer to actual interview questions.