ceph/src/boost/libs/spirit/include/boost/spirit/home/classic/core/composite/optional.hpp

   1 /*=============================================================================
   2     Copyright (c) 1998-2003 Joel de Guzman
   3     Copyright (c) 2001 Daniel Nuffer
   4     Copyright (c) 2002 Hartmut Kaiser
   5     http://spirit.sourceforge.net/
   6
   7   Distributed under the Boost Software License, Version 1.0. (See accompanying
   8   file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   9 =============================================================================*/
  10 #if !defined(BOOST_SPIRIT_OPTIONAL_HPP)
  11 #define BOOST_SPIRIT_OPTIONAL_HPP
  12
  13 #include <boost/spirit/home/classic/namespace.hpp>
  14 #include <boost/spirit/home/classic/core/parser.hpp>
  15 #include <boost/spirit/home/classic/core/primitives/primitives.hpp>
  16 #include <boost/spirit/home/classic/core/composite/composite.hpp>
  17 #include <boost/spirit/home/classic/meta/as_parser.hpp>
  18
  19 namespace boost { namespace spirit {
  20
  21 BOOST_SPIRIT_CLASSIC_NAMESPACE_BEGIN
  22
  23     ///////////////////////////////////////////////////////////////////////////
  24     //
  25     //  optional class
  26     //
  27     //      Handles expressions of the form:
  28     //
  29     //          !a
  30     //
  31     //      where a is a parser. The expression returns a composite
  32     //      parser that matches its subject zero (0) or one (1) time.
  33     //
  34     ///////////////////////////////////////////////////////////////////////////
  35     struct optional_parser_gen;
  36
  37     template <typename S>
  38     struct optional
  39     :   public unary<S, parser<optional<S> > >
  40     {
  41         typedef optional<S>                 self_t;
  42         typedef unary_parser_category       parser_category_t;
  43         typedef optional_parser_gen         parser_generator_t;
  44         typedef unary<S, parser<self_t> >   base_t;
  45
  46         optional(S const& a)
  47         : base_t(a) {}
  48
  49         template <typename ScannerT>
  50         typename parser_result<self_t, ScannerT>::type
  51         parse(ScannerT const& scan) const
  52         {
  53             typedef typename parser_result<self_t, ScannerT>::type result_t;
  54             typedef typename ScannerT::iterator_t iterator_t;
  55             iterator_t save = scan.first;
  56             if (result_t r = this->subject().parse(scan))
  57             {
  58                 return r;
  59             }
  60             else
  61             {
  62                 scan.first = save;
  63                 return scan.empty_match();
  64             }
  65         }
  66     };
  67
  68     struct optional_parser_gen
  69     {
  70         template <typename S>
  71         struct result
  72         {
  73             typedef optional<S> type;
  74         };
  75
  76         template <typename S>
  77         static optional<S>
  78         generate(parser<S> const& a)
  79         {
  80             return optional<S>(a.derived());
  81         }
  82     };
  83
  84     template <typename S>
  85     optional<S>
  86     operator!(parser<S> const& a);
  87
  88 BOOST_SPIRIT_CLASSIC_NAMESPACE_END
  89
  90 }} // namespace BOOST_SPIRIT_CLASSIC_NS
  91
  92 #endif
  93
  94 #include <boost/spirit/home/classic/core/composite/impl/optional.ipp>