Subject: Re: [PATCH] Make builtin-tag.c use parse_options.

From: Pierre Habouzit <[email-masked]>
Date: Sat, 10 Nov 2007 14:13:27 +0100

On Sat, Nov 10, 2007 at 12:25:44PM +0000, Carlos Rica wrote:
> 2007/11/10, Junio C Hamano <[email-masked]>:
> > Carlos Rica <[email-masked]> writes:

> A solution not needing memory allocation into the option parser
> could be setting a callback running over the repeated option
> arguments, passing them to the function one per each call.
> Then, the user will be able to decide if he wants the arguments
> concatenated or only need one of them and prefers erroring out.
> 
> Is this already possible with the current parser or the callback
> mode only calls using the last option?

  Everything is possible, you just have to code it. With a callback
you have in the struct option two places to store "things". The void*
value pointer and the intptr_t defval. _Usually_ the void* is the
pointer to the data that will be _written_ and the defval the data that
will be put into the void* under some circumstances (e.g. when your
option is negated).

  For Your case I'd go with some kind of string list pointed into the
void * value, defval has no or little use. You don't really care about
allocating memory in the option parser, I mean, option parsing is done
once at the initialization phase. It's not evil. In pseudo-C here is how
I would write the callback:

int parse_opt_stringlist(const struct option *opt, const char *arg, int unset)
{
    string_list **l = opt->value;
    string_list_elem *e;

    if (unset) { /* negationg option clears the list */
	while (*l) {
	    string_list_elem_free(string_list_pop(l));
	}
	return 0;
    }

    e = string_list_elem_new();
    e->data = arg;
    string_list_push(l, e);
    return 0;
}

  And you're done, you can do what you want with that list from the caller.
There probably is such a structure in git, if not, it can probably be hacked
in a few lines.

  Remember, callbacks give you _full_ control on what you can do in the option
parser, and if you're not happy with Turing complete expressivity, there isn't
anything I can do for you :P Note that if you do write such a generic
callback, it belongs to parse-options.[hc].

-- 
·O·  Pierre Habouzit
··O                                                [email-masked]
OOO                                                http://www.madism.org