"It's hard to transverse them, or to merge them, or often even to look up a list of keys." That's exactly what I'm arguing against in my comment on making your

"It's hard to transverse them, or to merge them, or often even to look up a list of keys." That's exactly what I'm arguing against in my comment on making your important structs/objects and their relationships explicit. Randomly mutating them together all over your program might seem more flexible but at a cost of making you worry about your code rather than your data definitions. And that's without even getting into performance implications. If you actually need a Map, of course, that's a different situation than the ones I'm thinking.