hello, relating to my earlier post, the code for the 2-seq and 3-seq cross product is: #include #include #include #include #include #include namespace mpl = boost::mpl; using namespace mpl::placeholders; template <typename T> struct pair_with : mpl::pair {}; template <typename pair> struct triple_with : mpl::vector3 {}; // public metafunction template struct sequence2_cross_product : mpl::fold< Sequence1, mpl::vector0<>, mpl::copy< mpl::transform< Sequence2, pair_with<_2> >, mpl::back_inserter<_1> >

{}; template< typename SequencePair, typename Sequence> struct seq_seqpair_product : mpl::fold< SequencePair, mpl::vector0<>, mpl::copy< mpl::transform< Sequence, triple_with<_2> >, mpl::back_inserter<_1> >

{}; // public metafunction template struct sequence3_cross_product : seq_seqpair_product< typename sequence2_cross_product::type, Sequence3> {}; usage is like: S1: any MPL sequence with T11, T12, T13...T1k types S2: any MPL sequence with T21, T22, T23...T2m types S3: any MPL sequence with T31, T32, T33...T3n types typedef sequence2_cross_product::type binary_product; /* this will be a mpl::vector< pair, pair, ... pair, pair, pair, ... pair > */ // and typedef sequence3_cross_product::type ternary_product; /* this will be same mpl::vector, but with vector3 ..... instead */ 1) I'm trying to make these metafunctions general enough, perhaps in the future i might use them for something i'm not thinking about now.... i would like to let the caller (me), choose what tuple/template to embed the resulting Tij, Tkl in... . for the sequence2_cross_product metafunction, mpl::pair, or mpl::vector2 or any class template that takes 2 type template arguments, or i could restrict the user to something that interacts well with mpl, is it "lambda expressions" or "metafct" or "metafct class"? . for the sequence3_cross_product metafunction, mpl::vector3 or any class template that takes 3 type template args... same question 2) I have a class template RT (not metafct or metafct class), that takes 3 template args, for each of these args, i have a list of possible types (in an mpl sequence), then i have a class R. I would like to define 2.1. typedef boost::variant< R, RT, RT.... > R; 2.2. do an explicit template instantiation of all the RT<..,..,..> Should i use Boost.PP for this, e.g.: #include #include #define Type1 (T11)(T12)(T13)...(T1k) #define Type2 (T21)(T22)(T23)...(T2k) #define Type3 (T31)(T32)(T33)...(T3k) #define M(r, product) template class RT; BOOST_PP_SEQ_FOR_EACH_PRODUCT(M, (Type1)(Type2)(Type3)) #undef Type1 #undef Type2 #undef Type3 #undef M and what about variant<...>, how would i write it with PP? comment, thoughsts are appreciated, thanks, regards,