add CCIO.with_in_out to read and write a file

src/io/CCIO.ml

@@ -173,6 +173,19 @@ let rec write_lines oc g = match g () with
 let write_lines_l oc l =
   List.iter (write_line oc) l
 
+let with_in_out ?(mode=0o644) ?(flags=[Open_creat]) filename f =
+  let ic = open_in_gen (Open_rdonly::flags) mode filename in
+  let oc = open_out_gen (Open_wronly::flags) mode filename in
+  try
+    let x = f ic oc in
+    close_out oc; (* must be first?! *)
+    close_in ic;
+    x
+  with e ->
+    close_out_noerr oc;
+    close_in_noerr ic;
+    raise e
+
 let tee funs g () = match g() with
   | None -> None
   | Some x as res ->

src/io/CCIO.mli

@@ -113,6 +113,14 @@ val write_lines : out_channel -> string gen -> unit
 
 val write_lines_l : out_channel -> string list -> unit
 
+(** {2 Both} *)
+
+val with_in_out : ?mode:int -> ?flags:open_flag list ->
+                  string -> (in_channel -> out_channel -> 'a) -> 'a
+(** Combines {!with_in} and {!with_out}.
+    @param flags opening flags (default [[Open_creat]])
+    @since NEXT_RELEASE *)
+
 (** {2 Misc for Generators} *)
 
 val tee : ('a -> unit) list -> 'a gen -> 'a gen