>If we now build a large list of objects, all with the same set of keys, then they can share a single key descriptor. This means that asymptotically maps will b

>If we now build a large list of objects, all with the same set of keys, then they can share a single key descriptor. This means that asymptotically maps will be as efficient in terms of storage as records. Credit for this idea comes from Richard O'Keefe who pointed this out years ago. I don’t think any other programming language does this, but I might be wrong. That is a nice language feature to enforce, I love it :) This is however basically the same thing that V8 / most Javascript runtimes do under the hood[1]. Essentially, as you construct objects and add/remove keys, you back them in the engine with more-efficient shared objects that have the same structure. Add a key D and it moves from <shared structure with A,B,C> to <shared structure with A,B,C,D>. Since most code ends up doing the same kind of operations on a bunch of similar bits of data, you can save a lot of compute-time by assuming that and having a slower fallback when it fails (like using an actual dictionary instead of a Struct-like thing). That said, Javascript has zero enforcement for this, and the runtimes may have already shifted to something different. They are quite different beasts. Just pointing out that the idea has been around. [1] it has been a while since I've looked closely, and I may be mistaken. Call it 95% certainty.