How can I find the size of `map` in ocaml? I am using `Map.Make` functor to create module?

Question

I could not find any size or len function in the official documentation. What is a simple way to find the number of elements in a map created using:

module M = Map.Make(String)

I am looking for something like M.size M.empty : 0.

Answer 1

The function that you're looking for is called cardinal (as in the cardinality of a set).

Example:

module M = Map.Make(String)

let m = M.singleton "x" "y"
let () = Printf.printf "%d\n" (M.cardinal m)

This will print 1, as there is exactly one binding.