keeper_matcher.hpp

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///////////////////////////////////////////////////////////////////////////////
// keeper_matcher.hpp
//
//  Copyright 2008 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_XPRESSIVE_DETAIL_CORE_MATCHER_KEEPER_MATCHER_HPP_EAN_10_04_2005
#define BOOST_XPRESSIVE_DETAIL_CORE_MATCHER_KEEPER_MATCHER_HPP_EAN_10_04_2005

// MS compatible compilers support #pragma once
#if defined(_MSC_VER) && (_MSC_VER >= 1020)
# pragma once
#endif

#include <boost/mpl/bool.hpp>
#include <boost/xpressive/detail/detail_fwd.hpp>
#include <boost/xpressive/detail/core/quant_style.hpp>
#include <boost/xpressive/detail/core/state.hpp>

namespace boost { namespace xpressive { namespace detail
{

    ///////////////////////////////////////////////////////////////////////////////
    // keeper_matcher
    //  Xpr can be either a static_xpression, or a shared_matchable
    template<typename Xpr>
    struct keeper_matcher
      : quant_style<quant_variable_width, unknown_width::value, Xpr::pure>
    {
        keeper_matcher(Xpr const &xpr, bool pure = Xpr::pure)
          : xpr_(xpr)
          , pure_(pure)
        {
        }

        template<typename BidiIter, typename Next>
        bool match(match_state<BidiIter> &state, Next const &next) const
        {
            return Xpr::pure || this->pure_
              ? this->match_(state, next, mpl::true_())
              : this->match_(state, next, mpl::false_());
        }

        template<typename BidiIter, typename Next>
        bool match_(match_state<BidiIter> &state, Next const &next, mpl::true_) const
        {
            BidiIter const tmp = state.cur_;

            // matching xpr is guaranteed to not produce side-effects, don't bother saving state
            if(!this->xpr_.match(state))
            {
                return false;
            }
            else if(next.match(state))
            {
                return true;
            }

            state.cur_ = tmp;
            return false;
        }

        template<typename BidiIter, typename Next>
        bool match_(match_state<BidiIter> &state, Next const &next, mpl::false_) const
        {
            BidiIter const tmp = state.cur_;

            // matching xpr could produce side-effects, save state
            memento<BidiIter> mem = save_sub_matches(state);

            if(!this->xpr_.match(state))
            {
                restore_action_queue(mem, state);
                reclaim_sub_matches(mem, state, false);
                return false;
            }
            restore_action_queue(mem, state);
            if(next.match(state))
            {
                reclaim_sub_matches(mem, state, true);
                return true;
            }

            restore_sub_matches(mem, state);
            state.cur_ = tmp;
            return false;
        }

        Xpr xpr_;
        bool pure_; // false if matching xpr_ could modify the sub-matches
    };

}}}

#endif