I'll repeat my usual comment about what I found annoying in Go: It seems like strings are basically the only data type of unlimited size that is supported as m

I'll repeat my usual comment about what I found annoying in Go: It seems like strings are basically the only data type of unlimited size that is supported as map keys (or at least that seemed to be the case a few years ago). I think that only types for which equality is defined in the language could be used as keys. Those types where numbers, characters and all other "small" fixed-size types, structs all of those members had equality defined, arrays of a type with equality, and strings. The size of an array is part of the type, so in that list of types with equality the only source of unlimited sizedness are strings. I guess that cover most cases where you want a type of unknown size as a key, but I found it pretty annoying. If you want to use, say, polynomials with integer coefficients as keys in a map, you'd have to either choose a fixed maximum size (degree, for example, or number of monomials) for the polynomials or convert back and forth between strings. It's not the only language that forces you to convert things to strings and back for use as map keys (AWK and Lua come to mind), but I wish it didn't have that limitation.