Thanks a lot for all your valuable hints!
I had a brief look at all of them.
It seems that most of them are a bit overkill for what I want, or would mean
some ugly messing with the symbol table through exporting imported
identifiers.
I like the straightforward approach that the user can choose at build time
to install either implementation, and can always come back on his decision.
Once the C version is installed, there is no reason to go back to the Perl
version - but it's possible (e.g. for testing of code destined for a
pure-Perl machine).
Also, many of your suggestions need Perl modules to be installed on the
target machine which do not exist on legacy Perl installations.
Since Date::Calc is such a low-level basic module, it should be especially
backward compatible, so that even people in old production environments
(never fix what ain't broken) can upgrade my module and benefit from new
functions, without having to install a load of other modules first - which
their company policies would probably not permit.
ExtUtils::CBuilder though seems a real winner, maybe I'll include this as an
optional way to determine that the C compiler is really present and working,
falling back to the method of scanning %Config and $ENV{PATH} if this module
is not available.
But first of all, I'll give it some more thought!
Thanks again to you all!
Cheers,
Steffen
