boost/accumulators/framework/accumulators/external_accumulator.hpp
///////////////////////////////////////////////////////////////////////////////
// external_accumulator.hpp
//
// Copyright 2005 Eric Niebler. Distributed under the Boost
// Software License, Version 1.0. (See accompanying file
// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
#ifndef BOOST_ACCUMULATORS_FRAMEWORK_ACCUMULATORS_EXTERNAL_ACCUMULATOR_HPP_EAN_01_12_2005
#define BOOST_ACCUMULATORS_FRAMEWORK_ACCUMULATORS_EXTERNAL_ACCUMULATOR_HPP_EAN_01_12_2005
#include <boost/mpl/placeholders.hpp>
#include <boost/parameter/keyword.hpp>
#include <boost/accumulators/framework/extractor.hpp>
#include <boost/accumulators/framework/depends_on.hpp> // for feature_tag
#include <boost/accumulators/framework/accumulator_base.hpp>
#include <boost/accumulators/framework/accumulators/reference_accumulator.hpp>
namespace boost { namespace accumulators { namespace impl
{
//////////////////////////////////////////////////////////////////////////
// external_impl
/// INTERNAL ONLY
///
template<typename Accumulator, typename Tag>
struct external_impl
: accumulator_base
{
typedef typename Accumulator::result_type result_type;
typedef typename detail::feature_tag<Accumulator>::type feature_tag;
external_impl(dont_care) {}
template<typename Args>
result_type result(Args const &args) const
{
return this->extract_(args, args[parameter::keyword<Tag>::instance | 0]);
}
private:
template<typename Args>
static result_type extract_(Args const &args, int)
{
// No named parameter passed to the extractor. Maybe the external
// feature is held by reference<>.
extractor<feature_tag> extract;
return extract(accumulators::reference_tag<Tag>(args));
}
template<typename Args, typename AccumulatorSet>
static result_type extract_(Args const &, AccumulatorSet const &acc)
{
// OK, a named parameter for this external feature was passed to the
// extractor, so use that.
extractor<feature_tag> extract;
return extract(acc);
}
};
} // namespace impl
namespace tag
{
//////////////////////////////////////////////////////////////////////////
// external
template<typename Feature, typename Tag, typename AccumulatorSet>
struct external
: depends_on<reference<AccumulatorSet, Tag> >
{
typedef
accumulators::impl::external_impl<
detail::to_accumulator<Feature, mpl::_1, mpl::_2>
, Tag
>
impl;
};
template<typename Feature, typename Tag>
struct external<Feature, Tag, void>
: depends_on<>
{
typedef
accumulators::impl::external_impl<
detail::to_accumulator<Feature, mpl::_1, mpl::_2>
, Tag
>
impl;
};
}
// for the purposes of feature-based dependency resolution,
// external_accumulator<Feature, Tag> provides the same feature as Feature
template<typename Feature, typename Tag, typename AccumulatorSet>
struct feature_of<tag::external<Feature, Tag, AccumulatorSet> >
: feature_of<Feature>
{
};
// Note: Usually, the extractor is pulled into the accumulators namespace with
// a using directive, not the tag. But the external<> feature doesn't have an
// extractor, so we can put the external tag in the accumulators namespace
// without fear of a name conflict.
using tag::external;
}} // namespace boost::accumulators
#endif