ceph/src/boost/boost/accumulators/framework/accumulators/external_accumulator.hpp

   1 ///////////////////////////////////////////////////////////////////////////////
   2 // external_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_EXTERNAL_ACCUMULATOR_HPP_EAN_01_12_2005
   9 #define BOOST_ACCUMULATORS_FRAMEWORK_ACCUMULATORS_EXTERNAL_ACCUMULATOR_HPP_EAN_01_12_2005
  10
  11 #include <boost/mpl/placeholders.hpp>
  12 #include <boost/parameter/keyword.hpp>
  13 #include <boost/accumulators/framework/extractor.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/accumulators/reference_accumulator.hpp>
  17
  18 namespace boost { namespace accumulators { namespace impl
  19 {
  20
  21     //////////////////////////////////////////////////////////////////////////
  22     // external_impl
  23     /// INTERNAL ONLY
  24     ///
  25     template<typename Accumulator, typename Tag>
  26     struct external_impl
  27       : accumulator_base
  28     {
  29         typedef typename Accumulator::result_type result_type;
  30         typedef typename detail::feature_tag<Accumulator>::type feature_tag;
  31
  32         external_impl(dont_care) {}
  33
  34         template<typename Args>
  35         result_type result(Args const &args) const
  36         {
  37             return this->extract_(args, args[parameter::keyword<Tag>::instance | 0]);
  38         }
  39
  40     private:
  41
  42         template<typename Args>
  43         static result_type extract_(Args const &args, int)
  44         {
  45             // No named parameter passed to the extractor. Maybe the external
  46             // feature is held by reference<>.
  47             extractor<feature_tag> extract;
  48             return extract(accumulators::reference_tag<Tag>(args));
  49         }
  50
  51         template<typename Args, typename AccumulatorSet>
  52         static result_type extract_(Args const &, AccumulatorSet const &acc)
  53         {
  54             // OK, a named parameter for this external feature was passed to the
  55             // extractor, so use that.
  56             extractor<feature_tag> extract;
  57             return extract(acc);
  58         }
  59     };
  60
  61 } // namespace impl
  62
  63 namespace tag
  64 {
  65     //////////////////////////////////////////////////////////////////////////
  66     // external
  67     template<typename Feature, typename Tag, typename AccumulatorSet>
  68     struct external
  69       : depends_on<reference<AccumulatorSet, Tag> >
  70     {
  71         typedef
  72             accumulators::impl::external_impl<
  73                 detail::to_accumulator<Feature, mpl::_1, mpl::_2>
  74               , Tag
  75             >
  76         impl;
  77     };
  78
  79     template<typename Feature, typename Tag>
  80     struct external<Feature, Tag, void>
  81       : depends_on<>
  82     {
  83         typedef
  84             accumulators::impl::external_impl<
  85                 detail::to_accumulator<Feature, mpl::_1, mpl::_2>
  86               , Tag
  87             >
  88         impl;
  89     };
  90 }
  91
  92 // for the purposes of feature-based dependency resolution,
  93 // external_accumulator<Feature, Tag> provides the same feature as Feature
  94 template<typename Feature, typename Tag, typename AccumulatorSet>
  95 struct feature_of<tag::external<Feature, Tag, AccumulatorSet> >
  96   : feature_of<Feature>
  97 {
  98 };
  99
 100 // Note: Usually, the extractor is pulled into the accumulators namespace with
 101 // a using directive, not the tag. But the external<> feature doesn't have an
 102 // extractor, so we can put the external tag in the accumulators namespace
 103 // without fear of a name conflict.
 104 using tag::external;
 105
 106 }} // namespace boost::accumulators
 107
 108 #endif