transformation/detail/replace.hpp

0001 /*=============================================================================
0002     Copyright (c) 2001-2011 Joel de Guzman
0003
0004     Distributed under the Boost Software License, Version 1.0. (See accompanying
0005     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0006 ==============================================================================*/
0007 #if !defined(FUSION_REPLACE_08182005_0841)
0008 #define FUSION_REPLACE_08182005_0841
0009
0010 #include <boost/fusion/support/config.hpp>
0011 #include <boost/type_traits/is_convertible.hpp>
0012 #include <boost/mpl/if.hpp>
0013 #include <boost/type_traits/remove_reference.hpp>
0014
0015 namespace boost { namespace fusion { namespace detail
0016 {
0017     template <bool is_convertible>
0018     struct replacer_helper;
0019
0020     template <>
0021     struct replacer_helper<false>
0022     {
0023         template <typename U, typename T>
0024         BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
0025         static U&
0026         call(U& x, T const&, T const&)
0027         {
0028             return x;
0029         }
0030     };
0031
0032     template <>
0033     struct replacer_helper<true>
0034     {
0035         template <typename U, typename T>
0036         BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
0037         static U
0038         call(U& x, T const& old_value, T const& new_value)
0039         {
0040             return (x == old_value) ? new_value : x;
0041         }
0042     };
0043
0044     template <typename T>
0045     struct replacer
0046     {
0047         BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
0048         replacer(T const& in_old_value, T const& in_new_value)
0049             : old_value(in_old_value), new_value(in_new_value) {}
0050
0051         template<typename Sig>
0052         struct result;
0053
0054         template <typename U1, typename U2>
0055         struct result<replacer<U1>(U2)>
0056         {
0057             typedef typename remove_reference<U2>::type value;
0058             typedef typename
0059                 mpl::if_<is_convertible<T, value>, value, value const&>::type
0060             type;
0061         };
0062
0063         template <typename U>
0064         BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
0065         typename result<replacer(U)>::type
0066         operator()(U const& x) const
0067         {
0068             return replacer_helper<is_convertible<T, U>::value>::
0069                 call(x, old_value, new_value);
0070         }
0071
0072         T old_value;
0073         T new_value;
0074     };
0075 }}}
0076
0077 #endif
0078