Hashtbl.Make vs. Hashtbl.create -- when to use what?

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@ninjaaron

which kinds of values would you recommend being comfortable with using with polymorphic compare and, more specificaly to this question, the generic hashing function?

Polymorphic compare is appropriate to use with values where the notion of “equality” you want is the same as “structural” equality. Things like ordinary variants, records, lists, arrays, primitives, etc. A data structure where this might not work correctly is, for example, binary search trees representing sets, where two different tree structures may still represent the same set of elements.

Jane Street’s libraries discourage the use of polymorphic compare altogether (see this thread for example).

@ninjaaron

do I really have to specify if I’m talking about the standard library?

I agree that if unspecified, it is reasonable to assume the standard library. My question was intended more as just a confirmation that we were talking about the same thing. Sorry if that was confusing.

@ninjaaron

And on that note, is Stdlib.Hashtbl.create similar to (Jane Street) Base.Hashtbl.Poly.create? (give or take a function. I didn’t bother to look up the exact function name.)

I believe so. That is the right function name. I think they use the same hash function, as well, although the tables themselves are represented differently.

Prost!