Variadic macros are part of the C99 standard. Judging from the preprocessor sources, their developers Mr Mensonides (and perhaps Mr Karvonen) seem to have painfully avoided breaking any rule of the C90 standard. For example, there are never empty macro arguments passed, although this would have simplified code in several instances.
So, using variadic macros will break downward compatibility.
I'm not sure I understand what you are saying.
Well, perhaps I should have written: Variadic macros are covered by C99 or later only, not by C90. So, whereever you want to introduce them, you have to provide a parallel C90 implementation, unless you want to exclude all non C99 conformant compilers. IMHO, if you use variadic macros to optimize internal processing for a subset of compilers, this is ok. But you must not expose them on the outside interface of BOOST_PP (such as to declare a new type), because that wouldn't be portable. And I am not sure whether BOOST_PP_ARRAY already covers much of the preprocessor type you had in mind.
I wasn't suggesting to use variadic macros in BOOST_PP_TUPLE_*, I meant new macros _like_ BOOST_PP_TUPLE_*. there are only 6 or so TUPLE macros, and their predominant use is probably: converting a tuple to a sequence.
Side note: I noticed they are often used as a sort of preprocessor struct, where you have cheap random access to 'members'.
that would effectively introducde a new "data type" to the PP library: a variadic tuple.
I'm sure I'm not the first to suggest this, but with the workaround submitted to that microsoft site MSVC can be supported (along with all compilers implementing (conforming) C99 variadic macros)
If you think it is time to leave C90 behind, it might be worth
no I don't.
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