I feel like many of the same principles from V8 (the engine for Chrome/Node.js) hidden classes would apply here. It's not just that you're interning keys; you'r

I feel like many of the same principles from V8 (the engine for Chrome/Node.js) hidden classes would apply here. It's not just that you're interning keys; you're actually creating a set of optimized data classes that are transitioned to when you encounter a key that wasn't seen before. In such a mode, you're not even storing the keys, just a pointer to the type information tree. Only when you have a sub-object whose keys are truly unpredictable do you go into "dictionary mode (aka 'slow mode')" - which I think says it all! https://v8.dev/docs/hidden-classes https://v8.dev/docs/hidden-classes