CCVector: Add function foldi

src/core/CCVector.ml

@@ -412,6 +412,18 @@ let fold f acc v =
   in
   fold acc 0
 
+let foldi f acc v =
+  let { vec; size } = v in
+  let rec fold acc i =
+    if i = size then
+      acc
+    else (
+      let x = Array.unsafe_get vec i in
+      fold (f i acc x) (i + 1)
+    )
+  in
+  fold acc 0
+
 let exists p v =
   let n = v.size in
   let rec check i =

src/core/CCVector.mli

@@ -206,6 +206,11 @@ val filter_in_place : ('a -> bool) -> ('a, rw) t -> unit
 val fold : ('b -> 'a -> 'b) -> 'b -> ('a, _) t -> 'b
 (** Fold on elements of the vector *)
 
+val foldi : (int -> 'b -> 'a -> 'b) -> 'b -> ('a, _) t -> 'b
+(** [foldi f init v] is just like {!fold}, but it also passes in the index
+    of each element as the first argument to the function [f].
+    @since NEXT_RELEASE *)
+
 val exists : ('a -> bool) -> ('a, _) t -> bool
 (** Existential test (is there an element that satisfies the predicate?). *)
 

tests/core/t_vector.ml

@@ -737,3 +737,17 @@ t @@ fun () -> of_list CCList.(1 -- 300_000) |> to_list = CCList.(1 -- 300_000)
 t @@ fun () ->
 let v = 1 -- 10 in
 to_list v = Gen.to_list (to_gen v)
+;;
+
+t @@ fun () ->
+let v = create () in
+0 = foldi (fun i acc _ -> acc + i) 0 v
+;;
+
+t @@ fun () ->
+let v = create () in
+push v 0;
+push v 0;
+push v 0;
+push v 0;
+6 = foldi (fun i acc _ -> acc + i) 0 v