> Date: Sun, 20 Jun 2010 18:02:16 -0700
> From: watanabesj@gmail.com
> To: boost-users@lists.boost.org
> Subject: Re: [Boost-users] preprocessor metaprogramming question
>
> AMDG
>
> Nathan Ridge wrote:
> >> Nathan Ridge wrote:
> >>
> >>>> MEMBERS((a)(b)(c))
> >>>>
> >>>>
> >>> I don't suppose there's any way to have the syntax be MEMBERS(a, b, c)?
> >>>
> >>>
> >> Not without variadic macros.
> >>
> >
> >
> > How would one do it using variadic macros?
> >
>
> I don't know, as I've never tried to use variadic macros.
> There ought to be some way to figure out how many
> argument you have. Once you have that, you can
> use Boost.PP tuples or arrays.

There appears to be no builtin way, but it turns out (http://groups.google.com/group/comp.std.c/browse_thread/thread/77ee8c8f92e4a3fb/346fc464319b1ee5)
you can write a macro that counts the number of arguments:
 
#define PP_NARG(...) \
         PP_NARG_(__VA_ARGS__,PP_RSEQ_N())
#define PP_NARG_(...) \
         PP_ARG_N(__VA_ARGS__)
#define PP_ARG_N( \
          _1, _2, _3, _4, _5, _6, _7, _8, _9,_10, \
         _11,_12,_13,_14,_15,_16,_17,_18,_19,_20, \
         _21,_22,_23,_24,_25,_26,_27,_28,_29,_30, \
         _31,_32,_33,_34,_35,_36,_37,_38,_39,_40, \
         _41,_42,_43,_44,_45,_46,_47,_48,_49,_50, \
         _51,_52,_53,_54,_55,_56,_57,_58,_59,_60, \
         _61,_62,_63,N,...) N
#define PP_RSEQ_N() \
         63,62,61,60,                   \
         59,58,57,56,55,54,53,52,51,50, \
         49,48,47,46,45,44,43,42,41,40, \
         39,38,37,36,35,34,33,32,31,30, \
         29,28,27,26,25,24,23,22,21,20, \
         19,18,17,16,15,14,13,12,11,10, \
         9,8,7,6,5,4,3,2,1,0
 
 
Is it possible to improve on this macro and write it in constant space with Boost.PP?
 
Thanks,
Nate.

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