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///////////////////////////////////////////////////////////////////////////////
/// \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
{}
};
// Additional specializations generated by the preprocessor
#include <boost/proto/context/detail/null_eval.hpp>
/// null_context
///
struct null_context
{
/// null_context::eval
///
template<typename Expr, typename ThisContext = null_context const>
struct eval
: null_eval<Expr, ThisContext>
{};
};
}}}
#endif
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