phoenix/core/value.hpp

0001 /*==============================================================================
0002     Copyright (c) 2001-2010 Joel de Guzman
0003     Copyright (c) 2010 Thomas Heller
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_PHOENIX_CORE_VALUE_HPP
0009 #define BOOST_PHOENIX_CORE_VALUE_HPP
0010
0011 #include <boost/phoenix/core/limits.hpp>
0012 #include <boost/phoenix/core/actor.hpp>
0013 #include <boost/phoenix/core/as_actor.hpp>
0014 #include <boost/phoenix/core/terminal.hpp>
0015 #include <boost/phoenix/core/is_value.hpp>
0016 #include <boost/utility/result_of.hpp>
0017
0018 namespace boost { namespace phoenix
0019 {
0020     ////////////////////////////////////////////////////////////////////////////
0021     //
0022     // values
0023     //
0024     //      function for evaluating values, e.g. val(123)
0025     //
0026     ////////////////////////////////////////////////////////////////////////////
0027
0028     namespace expression
0029     {
0030         template <typename T>
0031         struct value
0032             : expression::terminal<T>
0033         {
0034             typedef
0035                 typename expression::terminal<T>::type
0036                 type;
0037            /*
0038             static const type make(T & t)
0039             {
0040                 typename value<T>::type const e = {{t}};
0041                 return e;
0042             }
0043            */
0044         };
0045     }
0046
0047     template <typename T>
0048     inline
0049     typename expression::value<T>::type const
0050     val(T t)
0051     {
0052         return expression::value<T>::make(t);
0053     }
0054
0055     // Identifies this Expr as a value.
0056     // I think this is wrong. It is identifying all actors as values.
0057     // Yes, it is giving false positives and needs a rethink.
0058     // And this gives no positives.
0059     //template <typename T>
0060     //struct is_value<expression::value<T> >
0061     //    : mpl::true_
0062     //{};
0063
0064     // Call out actor for special handling
0065   // Is this correct? It applies to any actor.
0066   // In which case why is it here?
0067     template<typename Expr>
0068     struct is_custom_terminal<actor<Expr> >
0069       : mpl::true_
0070     {};
0071
0072     // Special handling for actor
0073     template<typename Expr>
0074     struct custom_terminal<actor<Expr> >
0075     {
0076         template <typename Sig>
0077         struct result;
0078
0079         template <typename This, typename Actor, typename Context>
0080         struct result<This(Actor, Context)>
0081             : boost::remove_const<
0082                     typename boost::remove_reference<
0083                     typename evaluator::impl<Actor, Context, proto::empty_env>::result_type
0084                  >::type
0085              >
0086         {};
0087
0088         template <typename Context>
0089         typename result<custom_terminal(actor<Expr> const &, Context &)>::type
0090         operator()(actor<Expr> const & expr, Context & ctx) const
0091         {
0092           typedef typename result<custom_terminal(actor<Expr> const &, Context &)>::type result_type;
0093           result_type r = boost::phoenix::eval(expr, ctx);
0094           // std::cout << "Evaluating val() = " << r << std::endl;
0095           return r;
0096         }
0097     };
0098
0099     namespace meta
0100     {
0101         template<typename T>
0102         struct const_ref
0103             : add_reference<typename add_const<T>::type>
0104         {};
0105
0106         template<typename T>
0107         struct argument_type
0108             : mpl::eval_if_c<
0109                 is_function<typename remove_pointer<T>::type>::value
0110               , mpl::identity<T>
0111               , const_ref<T>
0112             >
0113         {
0114             typedef T type;
0115         };
0116
0117         template <typename T>
0118         struct decay
0119         {
0120             typedef T type;
0121         };
0122         template <typename T, int N>
0123         struct decay<T[N]> : decay<T const *> {};
0124     }
0125
0126     template <typename T>
0127     struct as_actor<T, mpl::false_>
0128     {
0129         typedef typename expression::value<typename meta::decay<T>::type >::type type;
0130
0131         static type
0132         convert(typename meta::argument_type<typename meta::decay<T>::type>::type t)
0133         {
0134             return expression::value<typename meta::decay<T>::type >::make(t);
0135         }
0136     };
0137 }}
0138
0139 #endif