Subject: Re: [PATCH 2/2] make the ST_{C,M}TIME_NSEC macros more function like

From: Kjetil Barvik <[email-masked]>
Date: Sun, 15 Mar 2009 22:59:45 +0100

Junio C Hamano <[email-masked]> writes:

> Kjetil Barvik <[email-masked]> writes:
>
>> Make the macros take a pointer to a 'struct stat'. This is so that it
>> should be easier to understand what is going on, and that the macros
>> can later be implemented as a inline function if we want to.
>>
>> Impact: cosmetic change
>
> Hmm,...
>
> I have to wonder if this cosmetic change is an improvement, though.
>
> I do not have a strong feeling either way, but I think it makes it
> clear that these two macros are not lvalues if you do not pass a
> pointer but instead pass a structure.  An inline function can still
> take a structure passed by value as an argument anyway, no?

  It seems to woork from a small gcc test, but since C has call-by-
  value, and http://en.wikipedia.org/wiki/Call_by_value#Call_by_value
  says:

    [...] in C or Pascal, calling a function with a large structure as
    an argument will cause the entire structure to be copied,
    potentially causing serious performance degradation, and mutations
    to the structure are invisible to the caller. [...]

  So in my eyes it make more sense to be consistent and take the address
  of all struct like objects (&st in this case) for all arguments to
  "function-like" things.

  But, since these 2 are macros, which use textual substitution, I guess
  things will work correctly either way, and the compiled result will be
  the same.  But, I still like the more "function friendly" macros.

  -- kjetil