Casey Muratori – The Big OOPs: Anatomy of a Thirty-five-year Mistake – BSC 2025

Caption notes

Casey Muratori asks where to place encapsulation boundaries in software. He criticizes compile-time inheritance hierarchies that mirror domain objects. His Looking Glass example illustrates an alternative in which each system holds its own data and looks up records by entity ID. He uses Sketchpad to illustrate how operations across objects, such as solving constraints, may need access to data referenced by multiple objects. He sees a role for boundaries around genuinely separate processes. In the Q&A he also describes using tagged unions when states are mutually exclusive. This guide focuses on his spoken design argument. The historical account, slides and code details were not independently verified.