Ticket #2833: accu_b.hpp

#ifndef ACCU_B_HPP_INCLUDED
#define ACCU_B_HPP_INCLUDED

#include <boost/parameter/keyword.hpp>
#include <boost/mpl/void.hpp>
#include <boost/accumulators/framework/extractor.hpp>
#include <boost/accumulators/framework/accumulator_base.hpp>
#include <boost/accumulators/framework/extractor.hpp>
#include <boost/accumulators/numeric/functional.hpp>
#include <boost/accumulators/framework/parameters/sample.hpp>
#include <boost/accumulators/framework/depends_on.hpp>
#include <boost/accumulators/statistics_fwd.hpp>
#include <boost/shared_features/temp/accu_a.hpp>
namespace boost { namespace accumulators {


namespace impl
{
    ////////////////////////////////////////////////////////////////////////////
    // accu_b_impl
    template<typename Sample,typename Id0,typename Id1>
    class accu_b_impl
      : public accumulator_base
    {
        typedef  tag::accu_a<Id1>    a_type;
    public:
        typedef Sample result_type;
        template<typename Args>
        accu_b_impl(Args const &args)
        :x_(
            extract_result<a_type>(args[accumulator]) //returns garbage
        )
        {
        }

        accu_b_impl(const accu_b_impl& that)
        :x_(that.x_){}

        accu_b_impl& operator=(const accu_b_impl& that){
            if(&that!=this){
                x_ = that.x_;
            }
            return *this;
        }


        template<typename Args>
        void operator ()(Args const &args)
        {
            // overrides initialization
            x_ = extract_result<a_type>(args[accumulator]);
                }

        result_type result(dont_care) const
        {
          return x_;
        }

    private:
           result_type x_;
    };

} // namespace impl

///////////////////////////////////////////////////////////////////////////////
// tag::accu_b
//

namespace tag
{
    template <typename Id0,typename Id1=mpl::void_>
    struct accu_b
      : depends_on<tag::accu_a<Id1> >
    {
        /// INTERNAL ONLY
      typedef accumulators::impl::accu_b_impl<mpl::_1,Id0,Id1> impl;

    };
}


}} // namespace boost::accumulators

#endif