[diffxx]

The first two properties can be handled by adding optional fields to your struct. The third can be done at compile time rather than runtime if you define a strict class hierarchy. I think really the problem is that many languages make struct definition needlessly verbose so it feels convenient to just use a map. The price of using schemaless includes runtime performance as well as the compiler being unable to warn you about easy (for a compiler) to detect and report data mismatch errors. I have spent a lot of time using lua the way I think many people use clojure. It is quite seductive and does feel very productive at first, but eventually I find that for a sufficiently complex program, I want the compiler to validate my data usage for me.