[Boost.Preprocessor] FOREACH( MACRO, ... )
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
Daniel Larimer wrote:
Is there a reason why Boost.Preprocessor does not have many (any?) utilities for variadic macros? <snip> FOREACH( CASE, a, b, c, d, e) case a: case b: case c: case d: case e:
Isn't it what BOOST_PP_REPEAT and BOOST_PP_TUPLE is for ? -- ___________________________________________ Joel Falcou - Assistant Professor PARALL Team - LRI - Universite Paris Sud XI Tel : (+33)1 69 15 66 35
On Feb 16, 2010, at 1:53 AM, joel falcou wrote:
Daniel Larimer wrote:
Is there a reason why Boost.Preprocessor does not have many (any?) utilities for variadic macros? <snip> FOREACH( CASE, a, b, c, d, e) case a: case b: case c: case d: case e:
Isn't it what BOOST_PP_REPEAT and BOOST_PP_TUPLE is for ?
Clearly BOOST_PP_REPEAT is useful, but you need to know the number of arguments to successfully use it. Thus there need for PP_NARG(...), which for some reasons boost PP does not provide. So, I suppose that anyone with some experience with the pre-processor could come up with a FOREACH macro, it still seems much easer to write FOREACH(M,p1,p2,...) than what I have below (which is an improvement over what I sent before) #define PP_FOREACH_ARRAY( ... ) (PP_NARG(__VA_ARGS__) , ( __VA_ARGS__ ) ) #define PP_FOREACH_ELEM(z,n,data) BOOST_PP_ARRAY_ELEM( BOOST_PP_ADD(n,1), data ) #define PP_FOREACH( A, ... ) BOOST_PP_REPEAT( PP_NARG(__VA_ARGS__), PP_FOREACH_ELEM, PP_FOREACH_ARRAY(A,__VA_ARGS__) ) You will notice that even BOOST_PP_TOUBLE_TO_LIST( ) requires that you know the size first. Most developers do not know the preprocessor in and out and so a simple FOR_EACH() macro could help them.
-- ___________________________________________ Joel Falcou - Assistant Professor PARALL Team - LRI - Universite Paris Sud XI Tel : (+33)1 69 15 66 35
_______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
I now understand why Boost.Preprocessor doesn't support variable argument macros. Visual Studio has completely broken support and fails to expand __VA_ARGS__ into multiple tokens. Thus what works beautifully on G++ fails completely on VC++. Are there any known workarounds or will I need to ask the user of my macros to specify the number of arguments and then be limited to supporting the number of arguments I happen to enumerate? Dan On Feb 16, 2010, at 10:03 AM, Daniel Larimer wrote:
On Feb 16, 2010, at 1:53 AM, joel falcou wrote:
Daniel Larimer wrote:
Is there a reason why Boost.Preprocessor does not have many (any?) utilities for variadic macros? <snip> FOREACH( CASE, a, b, c, d, e) case a: case b: case c: case d: case e:
Isn't it what BOOST_PP_REPEAT and BOOST_PP_TUPLE is for ?
Clearly BOOST_PP_REPEAT is useful, but you need to know the number of arguments to successfully use it. Thus there need for PP_NARG(...), which for some reasons boost PP does not provide. So, I suppose that anyone with some experience with the pre-processor could come up with a FOREACH macro, it still seems much easer to write FOREACH(M,p1,p2,...) than what I have below (which is an improvement over what I sent before)
#define PP_FOREACH_ARRAY( ... ) (PP_NARG(__VA_ARGS__) , ( __VA_ARGS__ ) ) #define PP_FOREACH_ELEM(z,n,data) BOOST_PP_ARRAY_ELEM( BOOST_PP_ADD(n,1), data ) #define PP_FOREACH( A, ... ) BOOST_PP_REPEAT( PP_NARG(__VA_ARGS__), PP_FOREACH_ELEM, PP_FOREACH_ARRAY(A,__VA_ARGS__) )
You will notice that even BOOST_PP_TOUBLE_TO_LIST( ) requires that you know the size first.
Most developers do not know the preprocessor in and out and so a simple FOR_EACH() macro could help them.
-- ___________________________________________ Joel Falcou - Assistant Professor PARALL Team - LRI - Universite Paris Sud XI Tel : (+33)1 69 15 66 35
_______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
Daniel Larimer wrote:
I now understand why Boost.Preprocessor doesn't support variable argument macros. Visual Studio has completely broken support and fails to expand __VA_ARGS__ into multiple tokens. Thus what works beautifully on G++ fails completely on VC++.
Are there any known workarounds or will I need to ask the user of my macros to specify the number of arguments and then be limited to supporting the number of arguments I happen to enumerate?
Dan
...that, or accept Boost.PP seq's (i.e., "( arg0 ) ( arg1 ) ... ( argn )"), which I think is the direction many libraries that provide "variadic" macros take. - Jeff
participants (3)
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Daniel Larimer -
Jeffrey Hellrung -
joel falcou