more efficient CCString.init

src/core/CCString.cppo.ml

@@ -62,9 +62,8 @@ let init = String.init
 #else
 
 let init n f =
-  let buf = Buffer.create n in
-  for i = 0 to n-1 do Buffer.add_char buf (f i) done;
-  Buffer.contents buf
+  let buf = Bytes.init n f in
+  Bytes.unsafe_to_string buf
 
 #endif
 

src/core/CCString.mli

@@ -66,6 +66,11 @@ val init : int -> (int -> char) -> string
 (** Analog to [Array.init].
     @since 0.3.3 *)
 
+(*$T
+  init 3 (fun i -> [|'a'; 'b'; 'c'|].(i)) = "abc"
+  init 0 (fun _ -> assert false) = ""
+*)
+
 val of_gen : char gen -> string
 val of_seq : char sequence -> string
 val of_klist : char klist -> string