1 /////////////////////////////////////////////////////////////////////////////// 2 // reference_accumulator.hpp 3 // 4 // Copyright 2005 Eric Niebler. Distributed under the Boost 5 // Software License, Version 1.0. (See accompanying file 6 // LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 7 8 #ifndef BOOST_ACCUMULATORS_FRAMEWORK_ACCUMULATORS_REFERENCE_ACCUMULATOR_HPP_EAN_03_23_2006 9 #define BOOST_ACCUMULATORS_FRAMEWORK_ACCUMULATORS_REFERENCE_ACCUMULATOR_HPP_EAN_03_23_2006 10 11 #include <boost/ref.hpp> 12 #include <boost/mpl/always.hpp> 13 #include <boost/parameter/keyword.hpp> 14 #include <boost/accumulators/framework/depends_on.hpp> // for feature_tag 15 #include <boost/accumulators/framework/accumulator_base.hpp> 16 #include <boost/accumulators/framework/extractor.hpp> 17 18 namespace boost { namespace accumulators 19 { 20 21 namespace impl 22 { 23 ////////////////////////////////////////////////////////////////////////// 24 // reference_accumulator_impl 25 // 26 template<typename Referent, typename Tag> 27 struct reference_accumulator_impl 28 : accumulator_base 29 { 30 typedef Referent &result_type; 31 32 template<typename Args> reference_accumulator_implboost::accumulators::impl::reference_accumulator_impl33 reference_accumulator_impl(Args const &args) 34 : ref(args[parameter::keyword<Tag>::instance]) 35 { 36 } 37 resultboost::accumulators::impl::reference_accumulator_impl38 result_type result(dont_care) const 39 { 40 return this->ref; 41 } 42 43 private: 44 reference_wrapper<Referent> ref; 45 }; 46 } // namespace impl 47 48 namespace tag 49 { 50 ////////////////////////////////////////////////////////////////////////// 51 // reference_tag 52 template<typename Tag> 53 struct reference_tag 54 { 55 }; 56 57 ////////////////////////////////////////////////////////////////////////// 58 // reference 59 template<typename Referent, typename Tag> 60 struct reference 61 : depends_on<> 62 { 63 /// INTERNAL ONLY 64 /// 65 typedef mpl::always<accumulators::impl::reference_accumulator_impl<Referent, Tag> > impl; 66 }; 67 } 68 69 namespace extract 70 { 71 BOOST_ACCUMULATORS_DEFINE_EXTRACTOR(tag, reference, (typename)(typename)) 72 BOOST_ACCUMULATORS_DEFINE_EXTRACTOR(tag, reference_tag, (typename)) 73 } 74 75 using extract::reference; 76 using extract::reference_tag; 77 78 // Map all reference<V,T> features to reference_tag<T> so 79 // that references can be extracted using reference_tag<T> 80 // without specifying the referent type. 81 template<typename ValueType, typename Tag> 82 struct feature_of<tag::reference<ValueType, Tag> > 83 : feature_of<tag::reference_tag<Tag> > 84 { 85 }; 86 87 }} // namespace boost::accumulators 88 89 #endif 90