home/support/modify.hpp

0001 /*=============================================================================
0002   Copyright (c) 2001-2011 Joel de Guzman
0003   http://spirit.sourceforge.net/
0004
0005   Distributed under the Boost Software License, Version 1.0. (See accompanying
0006   file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0007 =============================================================================*/
0008 #ifndef BOOST_SPIRIT_MODIFY_OCTOBER_25_2008_0142PM
0009 #define BOOST_SPIRIT_MODIFY_OCTOBER_25_2008_0142PM
0010
0011 #if defined(_MSC_VER)
0012 #pragma once
0013 #endif
0014
0015 #include <boost/type_traits/is_base_of.hpp>
0016 #include <boost/spirit/home/support/unused.hpp>
0017
0018 namespace boost { namespace spirit
0019 {
0020     template <typename Domain, typename T, typename Enable = void>
0021     struct is_modifier_directive;
0022
0023     // Testing if a modifier set includes a modifier T involves
0024     // checking for inheritance (i.e. Modifiers is derived from T)
0025     template <typename Modifiers, typename T>
0026     struct has_modifier
0027         : is_base_of<T, Modifiers> {};
0028
0029     // Adding modifiers is done using multi-inheritance
0030     template <typename Current, typename New, typename Enable = void>
0031     struct compound_modifier : Current, New
0032     {
0033         compound_modifier()
0034           : Current(), New() {}
0035
0036         compound_modifier(Current const& current, New const& new_)
0037           : Current(current), New(new_) {}
0038     };
0039
0040     // Don't add if New is already in Current
0041     template <typename Current, typename New>
0042     struct compound_modifier<
0043         Current, New, typename enable_if<has_modifier<Current, New> >::type>
0044       : Current
0045     {
0046         compound_modifier()
0047           : Current() {}
0048
0049         compound_modifier(Current const& current, New const&)
0050           : Current(current) {}
0051     };
0052
0053     // Special case if Current is unused_type
0054     template <typename New, typename Enable>
0055     struct compound_modifier<unused_type, New, Enable> : New
0056     {
0057         compound_modifier()
0058           : New() {}
0059
0060         compound_modifier(unused_type, New const& new_)
0061           : New(new_) {}
0062     };
0063
0064     // Domains may specialize this modify metafunction to allow
0065     // directives to add information to the Modifier template
0066     // parameter that is passed to the make_component metafunction.
0067     // By default, we return the modifiers untouched
0068     template <typename Domain, typename Enable = void>
0069     struct modify
0070     {
0071         typedef void proto_is_callable_;
0072
0073         template <typename Sig>
0074         struct result;
0075
0076         template <typename This, typename Tag, typename Modifiers>
0077         struct result<This(Tag, Modifiers)>
0078         {
0079             typedef typename remove_const<
0080                 typename remove_reference<Tag>::type>::type
0081             tag_type;
0082             typedef typename remove_const<
0083                 typename remove_reference<Modifiers>::type>::type
0084             modifiers_type;
0085
0086             typedef typename mpl::if_<
0087                 is_modifier_directive<Domain, tag_type>
0088               , compound_modifier<modifiers_type, tag_type>
0089               , Modifiers>::type
0090             type;
0091         };
0092
0093         template <typename Tag, typename Modifiers>
0094         typename result<modify(Tag, Modifiers)>::type
0095         operator()(Tag tag, Modifiers modifiers) const
0096         {
0097             return op(tag, modifiers, is_modifier_directive<Domain, Tag>());
0098         }
0099
0100         template <typename Tag, typename Modifiers>
0101         Modifiers
0102         op(Tag /*tag*/, Modifiers modifiers, mpl::false_) const
0103         {
0104             return modifiers;
0105         }
0106
0107         template <typename Tag, typename Modifiers>
0108         compound_modifier<Modifiers, Tag>
0109         op(Tag tag, Modifiers modifiers, mpl::true_) const
0110         {
0111             return compound_modifier<Modifiers, Tag>(modifiers, tag);
0112         }
0113     };
0114 }}
0115
0116 #endif