On Mon, 24 Sep 2012 15:09:03 -0700, paul Fultz wrote:
#define SEQ (a,b,c)(1,2,3,4) BOOST_PP_VARIADIC_SEQ_TO_SEQ( SEQ ) // expands to ((a,b,c))((1,2,3,4))
In your implementations couldn't you use just two overload macros instead of 256? Like this:
# define BOOST_PP_VARIADIC_SEQ_TO_SEQ(seq) BOOST_PP_CAT( BOOST_PP_VARIADIC_SEQ_TO_SEQ_1_ seq, BOOST_PP_NIL )() # # define BOOST_PP_VARIADIC_SEQ_TO_SEQ_1_(...) (( __VA_ARGS__ )) BOOST_PP_VARIADIC_SEQ_TO_SEQ_2_ # define BOOST_PP_VARIADIC_SEQ_TO_SEQ_2_(...) (( __VA_ARGS__ )) BOOST_PP_VARIADIC_SEQ_TO_SEQ_1_
# define BOOST_PP_VARIADIC_SEQ_TO_SEQ_1_BOOST_PP_NIL() # define BOOST_PP_VARIADIC_SEQ_TO_SEQ_2_BOOST_PP_NIL()
Also on a side note, when vardiacs are enabled it would be nice to add an `IS_PAREN` macro like this:
Following the other similar macros that are already there, IS_NULLARY, IS_UNARY, and IS_BINARY, this would be named IS_N_ARY or IS_VARIADIC. However, what many people fail to realize is just how enormously difficult (and in some cases impossible) it is to modernize Boost.Preprocessor when support for VC++ (in particular) is required. It is usually easy to get a trivial case working. It is amazingly difficult to get non-trivial cases working because the nature of VC++'s macro replacement algorithm leads to combinatorial difficulties. E.g. It isn't that difficult to write macros A and B, test them individually to confirm that they work, but then some other macro C (possibly even written by a user) uses both and everything breaks. The point is that there is no black box testing. It is a *horrible* preprocessor. Edward has had some exposure to this when we worked on the limited variadic support that we did add. Besides the above, adding significant work to Boost.Preprocessor is iterating a dead horse. It is *way* outdated in terms of modern preprocessor metaprogramming technique. It needs a complete rewrite (i.e. it needs to be Chaos or similar to it) to support variadics properly. To modernize it, one has to abandon VC++'s preprocessor or somehow get MS to fix it (which is also beating a dead horse). There have been claims (on this list) that you can modernize it with current VC++, but, sorry, you can't. Not without throwing out a predictable, self-terminating recursion model. You could maybe get about a third of the way from Boost.Preprocessor to Chaos. Regards, Paul Mensonides