add CCVector.resize_with and CCVector.resize_with_init, tests and doc

src/core/CCVector.ml

@@ -201,6 +201,46 @@ let push v x =
   let v = of_list [1;2;3] in push v 4; to_list v = [1;2;3;4]
 *)
 
+let resize_with v f size =
+  if size > Sys.max_array_length then
+    invalid_arg "vec.resize_with: size too big"
+  else if size > Array.length v.vec then
+    let new_vec = Array.make size (f 0) in
+    Array.blit v.vec 0 new_vec 0 (v.size - 1);
+    for i = v.size to size - 1 do
+       Array.unsafe_set new_vec i (f i)
+     done;
+    v.vec <- new_vec;
+    v.size <- size
+
+(*$T
+  let v = make 1 0 in to_list (resize_with v (fun i -> i) 5) = [0;1;2;3;4]
+  let v = make 1 0 in length (resize_with v (fun i -> i) 5) = 5
+
+  let v = make 5 0 in to_list (resize_with v (fun i -> i) 5) = [0;0;0;0;0]
+  let v = make 5 0 in to_list (resize_with v (fun i -> i) 6) = [0;0;0;0;0;6]
+  let v = make 5 0 in to_list (resize_with v (fun i -> i) -1) = [0;0;0;0;0]
+  let v = make 5 0 in length (resize_with v (fun i -> i) 5) = 5
+*)
+
+let resize_with_init v ~init size =
+  if size > Sys.max_array_length then
+    invalid_arg "vec.resize_with_init: size too big"
+  else if size > Array.length v.vec then
+    let new_vec = Array.make size init in
+    Array.blit v.vec 0 new_vec 0 (v.size - 1);
+    v.vec <- new_vec;
+    v.size <- size
+
+(*$T
+  let v = make 1 0 in to_list (resize_with_init v ~init:1 5) = [1;1;1;1;1]
+  let v = make 1 0 in length (resize_with_init v ~init:1 5) = 5
+
+  let v = make 5 0 in to_list (resize_with_init v ~init:1 5) = [1;1;1;1;1]
+  let v = make 5 0 in to_list (resize_with_init v ~init:1 -1) = [1;1;1;1;1]
+  let v = make 5 0 in length (resize_with_init v ~init:1 5) = 5
+*)
+
 (** Add all elements of b to a *)
 let append a b =
   if array_is_empty_ a then (

src/core/CCVector.mli

@@ -79,6 +79,24 @@ val is_empty : ('a, _) t -> bool
 val push : ('a, rw) t -> 'a -> unit
 (** Add an element at the end of the vector. *)
 
+val resize_with : ('a, rw) t -> (int -> 'a) -> int -> unit
+(** [resize_with vec f size] resizes vector [vec] up to [size], fills vector
+    with calls to [f] on indexes [[vec.size-1.. size - 1]].
+    The contents and size of vec are untouched if [size] is inferior or equal
+    to [length vec].
+    @raise Invalid_argument if the size is too big
+
+    @since NEXT_RELEASE *)
+
+val resize_with_init : ('a, rw) t -> init:'a -> int -> unit
+(** [resize_with_init vec init size] resizes vector [vec] up to [size],
+    fills vector with calls to [init] on indexes [[length vec -1.. size - 1]].
+    The contents and size of vec are untouched if [size] is inferior or equal
+    to [length vec].
+    @raise Invalid_argument if the size is too big
+
+    @since NEXT_RELEASE *)
+
 val append : ('a, rw) t -> ('a, _) t -> unit
 (** [append a b] adds all elements of b to a. *)