keeper_matcher.hpp

来自「support vector clustering for vc++」· HPP 代码 · 共 98 行

///////////////////////////////////////////////////////////////////////////////
// keeper_matcher.hpp
//
//  Copyright 2004 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>
#include <boost/xpressive/detail/static/is_pure.hpp>

namespace boost { namespace xpressive { namespace detail
{

    ///////////////////////////////////////////////////////////////////////////////
    // keeper_matcher
    //       Xpr can be either a static_xpression, or a shared_ptr<matchable>
    template<typename Xpr>
    struct keeper_matcher
      : quant_style_auto<width_of<Xpr>, is_pure<Xpr> >
    {
        keeper_matcher(Xpr const &xpr, bool do_save = !is_pure<Xpr>::value)
          : xpr_(xpr)
          , do_save_(do_save)
        {
        }

        template<typename BidiIter, typename Next>
        bool match(state_type<BidiIter> &state, Next const &next) const
        {
            // Note that if is_pure<Xpr>::value is true, the compiler can tell which
            // branch to take.
            return is_pure<Xpr>::value || !this->do_save_
                ? this->match_(state, next, mpl::true_())
                : this->match_(state, next, mpl::false_());
        }

        template<typename BidiIter, typename Next>
        bool match_(state_type<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(!get_pointer(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_(state_type<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(!get_pointer(this->xpr_)->match(state))
            {
                reclaim_sub_matches(mem, state);
                return false;
            }
            else if(next.match(state))
            {
                reclaim_sub_matches(mem, state);
                return true;
            }

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

        Xpr xpr_;
        bool do_save_; // true if matching xpr_ could modify the sub-matches
    };

}}}

#endif