| 1 | //WARNING@2010-09-29:
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| 2 | // 1) Don't try to compile this code with that from:
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| 3 | /*
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| 4 | http://svn.boost.org/svn/boost/sandbox/variadic_templates/
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| 5 | */
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| 6 | // otherwise, you'll get a compile-time error about
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| 7 | // mpl::vector0.
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| 8 | //
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| 9 | // 2) Only works with variadic fusion:
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| 10 | /*
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| 11 | http://svn.boost.org/svn/boost/sandbox/SOC/2009/fusion/
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| 12 | */
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| 13 | // otherwise, you'll get compile-time error in category_of.hpp
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| 14 | // about joine_view<...>& not being class, struct, or union.
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| 15 | //
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| 16 | //Purpose:
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| 17 | // Answer question in post:
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| 18 | //
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| 19 | // http://article.gmane.org/gmane.comp.lib.boost.user/62386
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| 20 | //
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| 21 | //References:
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| 22 | // [ffold]
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| 23 | // http://www.boost.org/doc/libs/1_44_0/libs/fusion/doc/html
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| 24 | // /fusion/algorithm/iteration/functions/fold.html
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| 25 | //
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| 26 | #include <boost/fusion/algorithm/iteration/fold.hpp>
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| 27 | #include <boost/fusion/algorithm/transformation/join.hpp>
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| 28 | #include <boost/fusion/container/vector.hpp>
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| 29 | #include <boost/fusion/sequence/io.hpp>
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| 30 | #include <boost/utility/result_of.hpp>
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| 31 |
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| 32 | #include <iostream>
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| 33 |
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| 34 | namespace fold_join
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| 35 | {
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| 36 | struct join_ftor
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| 37 | /**@brief
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| 38 | * Forward decl of functor for joining 2 fusion sequences.
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| 39 | */
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| 40 | ;
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| 41 | template<typename T,unsigned Index=0>
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| 42 | struct tu
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| 43 | {
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| 44 | tu(T a_t):my_t(a_t){}
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| 45 | T my_t;
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| 46 |
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| 47 | friend
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| 48 | std::ostream&
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| 49 | operator<<
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| 50 | ( std::ostream& sout
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| 51 | , tu const& x
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| 52 | )
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| 53 | {
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| 54 | sout<<"tu<"<<Index<<">("<<x.my_t<<")";
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| 55 | return sout;
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| 56 | }
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| 57 | };
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| 58 |
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| 59 | }//exit fold_join namespace
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| 60 |
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| 61 | namespace boost
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| 62 | {
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| 63 | template
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| 64 | < typename LhSequence
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| 65 | , typename RhSequence
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| 66 | >
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| 67 | struct result_of
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| 68 | < fold_join::join_ftor(LhSequence,RhSequence)
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| 69 | >
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| 70 | /**@brief
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| 71 | * As specified by table 1.37 Requirement for Parameter f
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| 72 | * in [ffold].
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| 73 | */
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| 74 | : fusion::result_of::join<LhSequence, RhSequence>
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| 75 | {
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| 76 | };
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| 77 |
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| 78 | }//exit boost namespace
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| 79 |
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| 80 | namespace fold_join
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| 81 | {
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| 82 | struct join_ftor
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| 83 | /**@brief
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| 84 | * modified from 'struct make_string' from [ffold].
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| 85 | */
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| 86 | {
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| 87 | template<typename LhSequence, typename RhSequence>
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| 88 | typename boost::result_of<join_ftor(LhSequence,RhSequence)>::type
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| 89 | operator()(LhSequence& lhs, RhSequence& rhs)const
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| 90 | {
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| 91 | return boost::fusion::join(lhs,rhs);
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| 92 | }
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| 93 | };
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| 94 | }//exit fold_join namespace
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| 95 |
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| 96 | using namespace boost;
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| 97 | using namespace fold_join;
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| 98 |
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| 99 | int main(void)
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| 100 | {
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| 101 | typedef fusion::vector<> vec0;
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| 102 | typedef fusion::vector<tu<int,1>, tu<char,1>, tu<double,1> > t1;
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| 103 | typedef fusion::vector<tu<int,2>, tu<char,2>, tu<double,2> > t2;
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| 104 | typedef fusion::vector<tu<int,3>, tu<char,3>, tu<double,3> > t3;
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| 105 |
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| 106 | vec0 state0;
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| 107 | t1 v1(100,'b',300.1);
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| 108 | t2 v2(100,'b',300.1);
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| 109 | t3 v3(100,'b',300.1);
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| 110 | std::cout<<"v1="<<v1<<"\n";
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| 111 | std::cout<<"v2="<<v2<<"\n";
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| 112 | std::cout<<"v3="<<v3<<"\n";
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| 113 | fusion::vector<t1,t2,t3> vv(v1,v2,v3);
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| 114 | join_ftor joiner;
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| 115 | auto fold_vv=fusion::fold(vv,state0,joiner);
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| 116 | std::cout
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| 117 | <<"fold(vv,state0,join_ftor())="
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| 118 | <<fold_vv
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| 119 | <<"\n";
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| 120 | return 0;
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| 121 | }
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