[boost] [Boost.Preprocessor] FOREACH( MACRO, ... )

Subject: [boost] [Boost.Preprocessor] FOREACH( MACRO, ... )
From: Daniel Larimer (dlarimer_at_[hidden])
Date: 2010-02-15 22:48:48

Is there a reason why Boost.Preprocessor does not have many (any?) utilities for variadic macros?

I have implemented a FOREACH( MACRO, ... ) that results in the following expansion

MACRO(ARG1) MACRO(ARG2) ... 

Implemented as such:

#define FOREACH_ARRAY( ... )  (PP_NARG(__VA_ARGS__) , ( __VA_ARGS__ ) )

#define FOREACH( A, ... )  BOOST_PP_REPEAT( PP_NARG(__VA_ARGS__), A, FOREACH_ARRAY(__VA_ARGS__) )

#define CASE(z,n,data)    case BOOST_PP_ARRAY_ELEM( n, data ):

FOREACH( CASE, a, b, c, d, e)
case a: case b: case c: case d: case e:

Depends upon this macro:

#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