[BuildTools] Proposal: XXX_SVN_REV change from quoted string to numeric

[Stefan Vigerske]

Hi,

> 	One of the SCIP developers has run into a problem trying to identify
> exactly what version of clp is available.  In particular, he needs to be able to
> discriminate between revisions of the trunk, because of changes that are not
> backward compatible combined with additions of new features.
> 
> 	What he needs is a numeric constant to examine at compile time (as 
> opposed to a character string). XXX_VERSION is useless in trunk; it's set as
> #define XXX_VERSION "trunk"
> Even in stable or release, it's problematic because it's a quoted string.
> His proposal was to define a new constant
> #define XXX_NUMERIC_VERSION 42
> My objection, at least at the level of trunk, is that this will require manual 
> fussing. I countered by suggesting XXX_SVN_REV, which is meaningful for trunk, 
> stable, and release. 

But I'm not so sure that this will be useful for him, because changes to
old stables will also bump up the XXX_SVN_REV, so he cannot do something
like
#if XXX_SVN_REV >= 42
  // use new infeasible ray ... (my guess ;-))
#endif

> But it needs to change from
> #define XXX_SVN_REV "42"
> to
> #define XXX_SVN_REV  42
> (note the absence of quotes, so that it expands to a number that can be compared 
> at compile time). This change requires a bit of fussing in coin.m4 to make sure 
> that some of the more exotic output from svnversion is boiled down to a single 
> number, but that's no big thing.
> 
> 	Does anyone see a hazard? If not, I will commit this change to 
> BuildTools/trunk tomorrow (Sep. 3).

Apart from the above, having the revision number not quoted is a good
thing, I believe. Since it is always a number, it makes sense to have it
accessible as a number.

> 	Looking a bit further afield, what about XXX_VERSION?  Are people using
> it in a way that requires quoting the value?  I can see a much larger potential
> for problems with removing the quotes here.

One could make XXX_VERSION unquoted and define an XXX_VERSION_QUOTED for
convenience:
http://en.wikipedia.org/wiki/C_preprocessor#Indirectly_quoting_macro_arguments

So you could make this SCIP developer believe that he can write
#if CLP_VERSION >= 113   /* ??? */
to recognize when the changes he need made it into a stable version.
For trunk's, one may set the numerical XXX_VERSION to -1 or something
like that?

Stefan

-- 
Stefan Vigerske
Humboldt University Berlin, Numerical Mathematics
http://www.math.hu-berlin.de/~stefan