| #ifndef BOOST_PP_IS_ITERATING |
| /////////////////////////////////////////////////////////////////////////////// |
| /// \file null.hpp |
| /// Definintion of null_context\<\>, an evaluation context for |
| /// proto::eval() that simply evaluates each child expression, doesn't |
| /// combine the results at all, and returns void. |
| // |
| // Copyright 2008 Eric Niebler. Distributed under the Boost |
| // Software License, Version 1.0. (See accompanying file |
| // LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
| |
| #ifndef BOOST_PROTO_CONTEXT_NULL_HPP_EAN_06_24_2007 |
| #define BOOST_PROTO_CONTEXT_NULL_HPP_EAN_06_24_2007 |
| |
| #include <boost/preprocessor/iteration/iterate.hpp> |
| #include <boost/preprocessor/repetition/repeat.hpp> |
| #include <boost/proto/proto_fwd.hpp> |
| #include <boost/proto/eval.hpp> |
| #include <boost/proto/traits.hpp> |
| |
| namespace boost { namespace proto { namespace context |
| { |
| |
| template< |
| typename Expr |
| , typename Context |
| , long Arity // = Expr::proto_arity_c |
| > |
| struct null_eval |
| {}; |
| |
| template<typename Expr, typename Context> |
| struct null_eval<Expr, Context, 0> |
| { |
| typedef void result_type; |
| void operator()(Expr &, Context &) const |
| {} |
| }; |
| |
| #define BOOST_PROTO_EVAL_N(Z, N, DATA) \ |
| proto::eval(proto::child_c<N>(expr), ctx); \ |
| /**/ |
| |
| #define BOOST_PP_ITERATION_PARAMS_1 \ |
| (3, (1, BOOST_PROTO_MAX_ARITY, <boost/proto/context/null.hpp>)) \ |
| /**/ |
| |
| #include BOOST_PP_ITERATE() |
| |
| #undef BOOST_PROTO_EVAL_N |
| |
| /// null_context |
| /// |
| struct null_context |
| { |
| /// null_context::eval |
| /// |
| template<typename Expr, typename ThisContext = null_context const> |
| struct eval |
| : null_eval<Expr, ThisContext> |
| {}; |
| }; |
| |
| }}} |
| |
| #endif |
| |
| #else |
| |
| #define N BOOST_PP_ITERATION() |
| |
| template<typename Expr, typename Context> |
| struct null_eval<Expr, Context, N> |
| { |
| typedef void result_type; |
| |
| void operator ()(Expr &expr, Context &ctx) const |
| { |
| BOOST_PP_REPEAT(N, BOOST_PROTO_EVAL_N, ~) |
| } |
| }; |
| |
| #undef N |
| |
| #endif |