The type of the hashtable keys.

The equality predicate used to compare keys.

A hashing function on keys. It must be such that if two keys are equal according to equal, then they have identical hash values as computed by hash. Examples: suitable (equal, hash) pairs for arbitrary key types include

• ((=), Hashtbl.hash) for comparing objects by structure (provided objects do not contain floats)
• ((fun x y -> compare x y = 0), Hashtbl.hash) for comparing objects by structure and handling Stdlib.nan correctly
• ((==), Hashtbl.hash) for comparing objects by physical equality (e.g. for mutable or cyclic objects).