Hash_int
include Hash_gen.S with type key = int;
let create: int => t('a);
let clear: t('a) => unit;
let reset: t('a) => unit;
return the key found in the hashtbl. Use case: when you find the key existed in hashtbl, you want to use the one stored in the hashtbl. (they are semantically equivlanent, but may have other information different)
let length: t('a) => int;