Re: [PATCH v2] format-patch --signature-file <file>

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

Jeremiah Mahler <jmmahler@gmail.com> writes:

> On Sat, May 17, 2014 at 06:00:14AM -0400, Jeff King wrote:
>> 
>> If you wanted to know whether it was set, I guess you'd have to compare
>> it to the default, like:
>> 
>>   if (signature_file) {
>> 	if (signature && signature != git_version_string)
>> 		die("you cannot specify both a signature and a signature-file");
>> 	... read signature file ...
>>   }
>> 
>
> That works until someone changes the default value.
> But if they did that then some tests should fail.
>
> I like the address comparision which avoids a string comparision.

Well, "avoids" is not quite a correct phrasing, because !strcmp()
would be wrong there.  You cannot tell "the user did not set
anything and the variable stayed as the default" and "the user
explicitly gave us a string but it happened to be the same as the
default" apart with !strcmp().  Address comparison is not just
"avoids" but is the right thing to do in this case.

>> though it's a bit ugly that this code has to know what the default is.

Avoiding that is easy with an indirection, no?  Something like this
at the top:

  static const char *the_default_signature = git_version_string;
  static const char *signature = the_default_signature;

and comparing to see if signature points at the same address as
the_default_signature would give you what you want, I think.