add CCVector.shrink_to_fit to limit memory usage

src/core/CCVector.ml

@@ -453,6 +453,21 @@ let shrink v n =
   )
 *)
 
+let shrink_to_fit v : unit =
+  if v.size = 0 then (
+    v.vec <- [| |]
+  ) else if v.size < Array.length v.vec then (
+    v.vec <- Array.sub v.vec 0 v.size
+  )
+
+(*$QR
+  (gen Q.small_int) (fun v ->
+    let v' = copy v in
+    shrink_to_fit v;
+    to_list v = to_list v'
+  )
+*)
+
 let sort' cmp v =
   (* possibly copy array (to avoid junk at its end), then sort the array *)
   let a =

src/core/CCVector.mli

@@ -1,4 +1,3 @@
-
 (* This file is free software, part of containers. See file "license" for more details. *)
 
 (** {1 Growable, mutable vector} *)
@@ -124,6 +123,10 @@ val shrink : ('a, rw) t -> int -> unit
 (** Shrink to the given size (remove elements above this size).
     Does nothing if the parameter is bigger than the current size. *)
 
+val shrink_to_fit : ('a, _) t -> unit
+(** Shrink internal array to fit the size of the vector
+    @since NEXT_RELEASE *)
+
 val member : eq:('a -> 'a -> bool) -> 'a -> ('a, _) t -> bool
 (** Is the element a member of the vector? *)