Most languages have poor support for structural types though. If you try and join two records together (like a SQL join), what will your favourite language infer then?

dictionaries generally aren't guaranteed to contain an entry for every possible value of the key type. while you could implement the colors example with a dictionary, ideally you'd want the type system to assure that given a Color, there will be a string associated with it

It's not a dictionary (type-wise). "as const" is the magic ingredient.