A mutable map from keys of type 'a to values of type 'b.

create () returns a new, empty map. It does not allocate any storage until the first binding is added: empty maps are cheap.

length t is the number of bindings of t. Constant time.

is_empty t is length t = 0.

find t k returns the value bound to k.

• raises Not_found

  if k is not bound.

find_opt t k returns Some v if k is bound to v, None otherwise.

mem t k is true if k is bound in t.

add t k v binds k to v, replacing any existing binding.

add_if_new t k v binds k to v if k is not bound. Returns the previous binding: None if k was absent (it is now bound to v), Some v' if k was bound to v' (left unchanged).

add_overwrite t k v binds k to v, replacing any existing binding. Returns the previous binding: None if k was absent, Some v' if k was bound to v'.

remove t k removes the binding of k. Does nothing if k is not bound.

clear t removes all bindings of t, keeping its storage for reuse.

reset t removes all bindings of t and releases its storage: t is then as cheap as a new map.

iter f t applies f k v to each binding of t, in an unspecified order. f can look up t; if it modifies t, it is unspecified whether the added (or removed) bindings are visited, and which value is passed for an overwritten binding.

fold f t acc is f kN vN (... (f k1 v1 acc)), where (k1, v1) ... (kN, vN) are the bindings of t, in an unspecified order. Same restrictions as iter.