Re: [PATCH 2/3] convert "enum date_mode" into a struct

[Junio C Hamano <gitster@pobox.com>]

Jeff King <peff@peff.net> writes:

> ...  However, the tricky case is where we use the
> enum labels as constants, like:
>
>   show_date(t, tz, DATE_NORMAL);
>
> Ideally we could say:
>
>   show_date(t, tz, &{ DATE_NORMAL });
>
> but of course C does not allow that.
> ...
>   3. Provide a wrapper that generates the correct struct on
>      the fly. The big downside is that we end up pointing to
>      a single global, which makes our wrapper non-reentrant.
>      But show_date is already not reentrant, so it does not
>      matter.
>
> This patch implements 3, along with a minor macro to keep
> the size of the callers sane.

Another big downside is that DATE_NORMAL is defined to be "0".

This makes it very cumbersome to merge a side branch that uses an
outdated definition of show_date() and its friends and tell them
to show date normally.  The compiler does not help detecting
places that need to be adjusted during merge and instead just pass
a NULL pointer as a pointer to the new struct.