Benchmarks Are Free Now

My previous post walked through four bugs in ruby-enum, a gem I maintain, all stemming from the fact that class-level instance variables aren’t inherited by subclasses. The third fix, #59, made keys, key?, value?, key, value, to_h, parse and each walk up superclass and merge in a parent’s enums, so a subclass would see everything its ancestors defined. It was correct, fully tested, and shipped. It also made every one of those methods roughly 5x slower on any subclass. def _enum_hash if superclass < Ruby::Enum superclass.send(:_enum_hash).merge(_own_enum_hash) else _own_enum_hash end end This recomputes the merged hash, walking the entire ancestor chain, on every single call. There’s no caching. A one-level subclass calling .value pays for building a brand new hash, on top of the superclass doing the same, every time. The test suite didn’t notice because tests check correctness, not speed, and correctness was fine. I only found this because I asked Copilot CLI to add a benchmark script…