On 11/21/2010 4:40 AM, John Maddock wrote:
Why is there two mutually exclusive macros indicating variadic template support for gcc ?
There is the established BOOST_NO_VARIADIC_TEMPLATES which says that any compiler does not have variadic template support. Then I find that for gcc there is also BOOST_HAS_VARIADIC_TMPL which evidently says that the compiler does have variadic template support, and is in no other compiler header file than the gcc one. Since the two config macros are mutually exclusive in the gcc header file, why is there any need for BOOST_HAS_VARIADIC_TMPL ?
Historical baggage - the BOOST_HAS_ one is deprecated and no longer documented, new code should always be using the BOOST_NO_ version, the other is present for backwards compatibility. BTW I've just committed a fix to Trunk to make sure that the two versions are normalized with respect to each other. If someone wants to take on the task of getting the release branch free of the BOOST_HAS_ version, then they can also remove it from Boost.Config ;-)
I only found the BOOST_HAS_VARIADIC_TMPL defined in the gcc.hpp file. There are also tests for it in config, as well as tests for the absence of BOOST_NO_VARIADIC_TEMPLATES, and the tests are exactly the same ( created by Doug Gregor ). As I remember your system of generating tests for config, once the .ipp file is removed everything works properly after that. The only place I found it is used outside of config is in Peter Dimov's make_shared and some files connected to that. It does seem as if changing his use of '#if defined( BOOST_HAS_VARIADIC_TMPL )' to '#if !defined( BOOST_NO_VARIADIC_TEMPLATES )' in his file and test is straightforward. I can take on that task but I do not believe I have write access to Boost trunk unless my access to the Boost sandbox gives me that. I can of course send you many svn patches if you like. I'd have to look at shared_ptr regressions test, as well as config regression tests, to make sure there is no unexpected failures once the changes are made.