Hashtable with a simple polymorphic type, but without the polymorphic equality.
This module re-wraps the hashtable implementation provided by Hashtbl.Make under a different interface: we just have a single type ('k, 'v) t, similar to a polymorphic hashtable.
This means that if you want a hash table generic over the type of keys, you don't have to put your type inside a functor.
Unlike the polymorphich hashtable (('k, 'v) Hashtbl.t), this does not use polymorphic hash and polymorphic equality, so this module does respect abstraction boundaries.
module type Key = sig ... endval find : ('k, 'v) t -> 'k -> 'v optionval find_exn : ('k, 'v) t -> 'k -> 'vval set : ('k, 'v) t -> 'k -> 'v -> unitval add_exn : ('k, 'v) t -> 'k -> 'v -> unitval clear : ('k, 'v) t -> unitval mem : ('k, _) t -> 'k -> boolval keys : ('k, _) t -> 'k listval foldi : ('k, 'v) t -> init:'init -> f:('k -> 'v -> 'init -> 'init) -> 'initval fold : (_, 'v) t -> init:'init -> f:('v -> 'init -> 'init) -> 'initval find_or_add : ('k, 'v) t -> 'k -> f:('k -> 'v) -> 'vval remove : ('k, _) t -> 'k -> unitval iter : (_, 'v) t -> f:('v -> unit) -> unitval filteri_inplace : ('a, 'b) t -> f:(key:'a -> data:'b -> bool) -> unitval length : (_, _) t -> int