Libguestfs - Aug 2009 - factorization would be nice

Hi Rich,

I've changed part of generator.ml to look like this:

      (match snd style with
       | [] -> ()
       | args ->
           pr "  memset (&args, 0, sizeof args);\n";
           pr "\n";
           pr "  if (!xdr_guestfs_%s_args (xdr_in, &args)) {\n"
name;
           pr "    reply_with_error (\"%%s: daemon failed to decode
procedure arguments\", \"%s\");\n" name;
           pr "    return;\n";
           pr "  }\n";
           List.iter (
             function
             | Pathname n ->
                 pr "  char *%s = args.%s;\n" n n;
                 pr "  ABS_PATH (%s, goto done);\n" n;
             | Device n ->
                 pr "  char *%s = args.%s;\n" n n;
                 pr "  RESOLVE_DEVICE (%s, goto done);" n;
	     | Dev_or_Path n ->
                 pr "  char *%s = args.%s;\n" n n;
                 pr "  REQUIRE_ROOT_OR_RESOLVE_DEVICE (%s, goto
done);" n;
             | String n -> pr "  char *%s = args.%s;\n" n n
             | OptString n -> pr "  %s = args.%s ? *args.%s :
NULL;\n" n n n
             | StringList n ->
                 pr "  %s = realloc (args.%s.%s_val,\n" n n n;
                 pr "                sizeof (char *) *
(args.%s.%s_len+1));\n" n n;
                 pr "  if (%s == NULL) {\n" n;
                 pr "    reply_with_perror
(\"realloc\");\n";
                 pr "    goto done;\n";
                 pr "  }\n";
                 pr "  %s[args.%s.%s_len] = NULL;\n" n n n;
                 pr "  args.%s.%s_val = %s;\n" n n n;
             | Bool n -> pr "  %s = args.%s;\n" n n
             | Int n -> pr "  %s = args.%s;\n" n n
             | FileIn _ | FileOut _ -> ()
           ) args;
           pr "\n"
      );

Note the 4-x repeated statement:

                 pr "  char *%s = args.%s;\n" n n;

What's the best way to avoid that?

On Wed, Aug 12, 2009 at 10:07:16AM +0200, Jim Meyering
wrote:
> Hi Rich,
> 
> I've changed part of generator.ml to look like this:
> 
>       (match snd style with
>        | [] -> ()
>        | args ->
>            pr "  memset (&args, 0, sizeof args);\n";
>            pr "\n";
>            pr "  if (!xdr_guestfs_%s_args (xdr_in, &args))
{\n" name;
>            pr "    reply_with_error (\"%%s: daemon failed to
decode procedure arguments\", \"%s\");\n" name;
>            pr "    return;\n";
>            pr "  }\n";
>            List.iter (
>              function
>              | Pathname n ->
>                  pr "  char *%s = args.%s;\n" n n;
>                  pr "  ABS_PATH (%s, goto done);\n" n;
>              | Device n ->
>                  pr "  char *%s = args.%s;\n" n n;
>                  pr "  RESOLVE_DEVICE (%s, goto done);" n;
> 	     | Dev_or_Path n ->
>                  pr "  char *%s = args.%s;\n" n n;
>                  pr "  REQUIRE_ROOT_OR_RESOLVE_DEVICE (%s, goto
done);" n;
>              | String n -> pr "  char *%s = args.%s;\n" n n
>              | OptString n -> pr "  %s = args.%s ? *args.%s :
NULL;\n" n n n
>              | StringList n ->
>                  pr "  %s = realloc (args.%s.%s_val,\n" n n n;
>                  pr "                sizeof (char *) *
(args.%s.%s_len+1));\n" n n;
>                  pr "  if (%s == NULL) {\n" n;
>                  pr "    reply_with_perror
(\"realloc\");\n";
>                  pr "    goto done;\n";
>                  pr "  }\n";
>                  pr "  %s[args.%s.%s_len] = NULL;\n" n n n;
>                  pr "  args.%s.%s_val = %s;\n" n n n;
>              | Bool n -> pr "  %s = args.%s;\n" n n
>              | Int n -> pr "  %s = args.%s;\n" n n
>              | FileIn _ | FileOut _ -> ()
>            ) args;
>            pr "\n"
>       );
> 
> Note the 4-x repeated statement:
> 
>                  pr "  char *%s = args.%s;\n" n n;
> 
> What's the best way to avoid that?
Just created a nested function:

  let pr_args n     pr "  char *%s = args.%s;\n" n n
  in

  (* ... *)
  pr_args n

You can create functions anywhere, at any level of nesting, even
inside expressions, and nested functions are common and a Good Thing.

Rich.

-- 
Richard Jones, Emerging Technologies, Red Hat  http://et.redhat.com/~rjones
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