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///////////////////////////////////////////////////////////////////////////////
// reference_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_REFERENCE_ACCUMULATOR_HPP_EAN_03_23_2006
#define BOOST_ACCUMULATORS_FRAMEWORK_ACCUMULATORS_REFERENCE_ACCUMULATOR_HPP_EAN_03_23_2006
#include <boost/ref.hpp>
#include <boost/mpl/always.hpp>
#include <boost/parameter/keyword.hpp>
#include <boost/accumulators/framework/depends_on.hpp> // for feature_tag
#include <boost/accumulators/framework/accumulator_base.hpp>
#include <boost/accumulators/framework/extractor.hpp>
namespace boost { namespace accumulators
{
namespace impl
{
//////////////////////////////////////////////////////////////////////////
// reference_accumulator_impl
//
template<typename Referent, typename Tag>
struct reference_accumulator_impl
: accumulator_base
{
typedef Referent &result_type;
template<typename Args>
reference_accumulator_impl(Args const &args)
: ref(args[parameter::keyword<Tag>::get()])
{
}
result_type result(dont_care) const
{
return this->ref;
}
private:
reference_wrapper<Referent> ref;
};
} // namespace impl
namespace tag
{
//////////////////////////////////////////////////////////////////////////
// reference_tag
template<typename Tag>
struct reference_tag
{
};
//////////////////////////////////////////////////////////////////////////
// reference
template<typename Referent, typename Tag>
struct reference
: depends_on<>
{
/// INTERNAL ONLY
///
typedef mpl::always<accumulators::impl::reference_accumulator_impl<Referent, Tag> > impl;
};
}
namespace extract
{
BOOST_ACCUMULATORS_DEFINE_EXTRACTOR(tag, reference, (typename)(typename))
BOOST_ACCUMULATORS_DEFINE_EXTRACTOR(tag, reference_tag, (typename))
}
using extract::reference;
using extract::reference_tag;
// Map all reference<V,T> features to reference_tag<T> so
// that references can be extracted using reference_tag<T>
// without specifying the referent type.
template<typename ValueType, typename Tag>
struct feature_of<tag::reference<ValueType, Tag> >
: feature_of<tag::reference_tag<Tag> >
{
};
}} // namespace boost::accumulators
#endif
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