Hi, some of you might like this pattern - it might be even practical at places... Maybe it's new, at least I couldn't find anything about it on the web. Regards, Tobias // read bottom up // ---- "library" code #include <boost/preprocessor/comparison/equal.hpp> #include <boost/preprocessor/control/iif.hpp> #include <boost/preprocessor/tuple/elem.hpp> #include <boost/preprocessor/cat.hpp> // public #define ARG(i,args,deflt) \ BOOST_PP_TUPLE_ELEM(2,1,BOOST_PP_CAT(SEARCH_A_ ## i args (i,deflt),_END)) // private #define SEARCH_A_0(k,v) BOOST_PP_IIF(BOOST_PP_EQUAL(0,k),(k,v) SKIP_A, SEARCH_B_0) #define SEARCH_B_0(k,v) BOOST_PP_IIF(BOOST_PP_EQUAL(0,k),(k,v) SKIP_A, SEARCH_A_0) #define SEARCH_A_1(k,v) BOOST_PP_IIF(BOOST_PP_EQUAL(1,k),(k,v) SKIP_A, SEARCH_B_1) #define SEARCH_B_1(k,v) BOOST_PP_IIF(BOOST_PP_EQUAL(1,k),(k,v) SKIP_A, SEARCH_A_1) #define SEARCH_A_2(k,v) BOOST_PP_IIF(BOOST_PP_EQUAL(2,k),(k,v) SKIP_A, SEARCH_B_2) #define SEARCH_B_2(k,v) BOOST_PP_IIF(BOOST_PP_EQUAL(2,k),(k,v) SKIP_A, SEARCH_A_2) // ... #define SKIP_A(k,v) SKIP_B #define SKIP_B(k,v) SKIP_A #define SKIP_A_END #define SKIP_B_END // ---- macro with named parameters example // public #define MY_FIRST_ARG(value) (0,value) #define MY_SECOND_ARG(value) (1,value) #define MY_THIRD_ARG(value) (2,value) #define MY_MACRO(args) \ MY_MACRO_IMPL( ARG(0,args,1st_default), ARG(1,args,2nd_default), ARG(2,args,3rd_default) ) // private #define MY_MACRO_IMPL(arg1,arg2,arg3) \ arg1 arg2 arg3 // note: parameter names can be reused among macros // ---- client code MY_MACRO( MY_FIRST_ARG(yaba) MY_THIRD_ARG(doo) MY_SECOND_ARG(daba) ) // expands to: yaba daba doo MY_MACRO( MY_SECOND_ARG(bubu) ) // expands to: 1st_default bubu 3rd_default.