core/matcher/keeper_matcher.hpp

0001 ///////////////////////////////////////////////////////////////////////////////
0002 // keeper_matcher.hpp
0003 //
0004 //  Copyright 2008 Eric Niebler. Distributed under the Boost
0005 //  Software License, Version 1.0. (See accompanying file
0006 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0007
0008 #ifndef BOOST_XPRESSIVE_DETAIL_CORE_MATCHER_KEEPER_MATCHER_HPP_EAN_10_04_2005
0009 #define BOOST_XPRESSIVE_DETAIL_CORE_MATCHER_KEEPER_MATCHER_HPP_EAN_10_04_2005
0010
0011 // MS compatible compilers support #pragma once
0012 #if defined(_MSC_VER)
0013 # pragma once
0014 #endif
0015
0016 #include <boost/mpl/bool.hpp>
0017 #include <boost/xpressive/detail/detail_fwd.hpp>
0018 #include <boost/xpressive/detail/core/quant_style.hpp>
0019 #include <boost/xpressive/detail/core/state.hpp>
0020
0021 namespace boost { namespace xpressive { namespace detail
0022 {
0023
0024     ///////////////////////////////////////////////////////////////////////////////
0025     // keeper_matcher
0026     //  Xpr can be either a static_xpression, or a shared_matchable
0027     template<typename Xpr>
0028     struct keeper_matcher
0029       : quant_style<quant_variable_width, unknown_width::value, Xpr::pure>
0030     {
0031         keeper_matcher(Xpr const &xpr, bool pure = Xpr::pure)
0032           : xpr_(xpr)
0033           , pure_(pure)
0034         {
0035         }
0036
0037         template<typename BidiIter, typename Next>
0038         bool match(match_state<BidiIter> &state, Next const &next) const
0039         {
0040             return Xpr::pure || this->pure_
0041               ? this->match_(state, next, mpl::true_())
0042               : this->match_(state, next, mpl::false_());
0043         }
0044
0045         template<typename BidiIter, typename Next>
0046         bool match_(match_state<BidiIter> &state, Next const &next, mpl::true_) const
0047         {
0048             BidiIter const tmp = state.cur_;
0049
0050             // matching xpr is guaranteed to not produce side-effects, don't bother saving state
0051             if(!this->xpr_.match(state))
0052             {
0053                 return false;
0054             }
0055             else if(next.match(state))
0056             {
0057                 return true;
0058             }
0059
0060             state.cur_ = tmp;
0061             return false;
0062         }
0063
0064         template<typename BidiIter, typename Next>
0065         bool match_(match_state<BidiIter> &state, Next const &next, mpl::false_) const
0066         {
0067             BidiIter const tmp = state.cur_;
0068
0069             // matching xpr could produce side-effects, save state
0070             memento<BidiIter> mem = save_sub_matches(state);
0071
0072             if(!this->xpr_.match(state))
0073             {
0074                 restore_action_queue(mem, state);
0075                 reclaim_sub_matches(mem, state, false);
0076                 return false;
0077             }
0078             restore_action_queue(mem, state);
0079             if(next.match(state))
0080             {
0081                 reclaim_sub_matches(mem, state, true);
0082                 return true;
0083             }
0084
0085             restore_sub_matches(mem, state);
0086             state.cur_ = tmp;
0087             return false;
0088         }
0089
0090         Xpr xpr_;
0091         bool pure_; // false if matching xpr_ could modify the sub-matches
0092     };
0093
0094 }}}
0095
0096 #endif