Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16: /// \file null.hpp
Chris@16: /// Definintion of null_context\<\>, an evaluation context for
Chris@16: /// proto::eval() that simply evaluates each child expression, doesn't
Chris@16: /// combine the results at all, and returns void.
Chris@16: //
Chris@16: //  Copyright 2008 Eric Niebler. Distributed under the Boost
Chris@16: //  Software License, Version 1.0. (See accompanying file
Chris@16: //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
Chris@16: 
Chris@16: #ifndef BOOST_PROTO_CONTEXT_NULL_HPP_EAN_06_24_2007
Chris@16: #define BOOST_PROTO_CONTEXT_NULL_HPP_EAN_06_24_2007
Chris@16: 
Chris@16: #include <boost/preprocessor/iteration/iterate.hpp>
Chris@16: #include <boost/preprocessor/repetition/repeat.hpp>
Chris@16: #include <boost/proto/proto_fwd.hpp>
Chris@16: #include <boost/proto/eval.hpp>
Chris@16: #include <boost/proto/traits.hpp>
Chris@16: 
Chris@16: namespace boost { namespace proto { namespace context
Chris@16: {
Chris@16: 
Chris@16:     template<
Chris@16:         typename Expr
Chris@16:       , typename Context
Chris@16:       , long Arity          // = Expr::proto_arity_c
Chris@16:     >
Chris@16:     struct null_eval
Chris@16:     {};
Chris@16: 
Chris@16:     template<typename Expr, typename Context>
Chris@16:     struct null_eval<Expr, Context, 0>
Chris@16:     {
Chris@16:         typedef void result_type;
Chris@16:         void operator()(Expr &, Context &) const
Chris@16:         {}
Chris@16:     };
Chris@16: 
Chris@16:     // Additional specializations generated by the preprocessor
Chris@16:     #include <boost/proto/context/detail/null_eval.hpp>
Chris@16: 
Chris@16:     /// null_context
Chris@16:     ///
Chris@16:     struct null_context
Chris@16:     {
Chris@16:         /// null_context::eval
Chris@16:         ///
Chris@16:         template<typename Expr, typename ThisContext = null_context const>
Chris@16:         struct eval
Chris@16:           : null_eval<Expr, ThisContext>
Chris@16:         {};
Chris@16:     };
Chris@16: 
Chris@16: }}}
Chris@16: 
Chris@16: #endif