Re: [PATCH 1/2] parse-options: add int value pointer to struct option

From: Junio C Hamano <gitster@pobox.com>
Date: Sep 11, 2023, 19:19 UTC
Message-ID: <xmqq7cowv7pm.fsf@gitster.g>
In-Reply-To: <ZP4NrVeqMtFTLEuf@nand.local>

Taylor Blau <me@ttaylorr.com> writes:

Show 14 quoted lines

> callback, something like:
>
>     struct option {
>         /* ... */
>         union {
>             void *value;
>             int *value_int;
>             /* etc ... */
>         } u;
>         enum option_type t;
>     };
>
> where option_type has some value corresponding to "void *", another for
> "int *", and so on.

Yup, that does cross my mind, even though I would have used

	union {
		void *void_ptr;
		int *int_ptr;
	} value;

or something without a rather meaningless 'u'.

Show 6 quoted lines

> Alternatively, perhaps you are thinking that we'd use both the value
> pointer and the value_int pointer to point at potentially different
> values in the same callback. I don't have strong feelings about it, but
> I'd just as soon encourage us to shy away from that approach, since
> assigning a single callback parameter to each function seems more
> organized.

We have seen (with Peff's "-Wunused" work) that there are small number of cases that it would be handy for a callback to be told the locations of multiple external variables, but I do not think it would be a good solution to that problem to have "void *value" and "int value_int" next to each other and allow them to coexist, as it would work only when these multiple variables happen to be of the right types.