Update of /cvsroot/boost/boost/boost/xpressive/proto/transform
In directory sc8-pr-cvs3.sourceforge.net:/tmp/cvs-serv30998/proto/transform
Added Files:
conditional.hpp
Log Message:
as_optional transform, and proto::trans::conditional
--- NEW FILE: conditional.hpp ---
///////////////////////////////////////////////////////////////////////////////
/// \file conditional.hpp
/// A special-purpose proto transform for selecting between two transforms
/// based on a compile-time predicate.
//
// Copyright 2004 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_TRANSFORM_CONDITIONAL_HPP_EAN_04_02_2007
#define BOOST_PROTO_TRANSFORM_CONDITIONAL_HPP_EAN_04_02_2007
#include <boost/xpressive/proto/detail/prefix.hpp>
#include <boost/mpl/assert.hpp>
#include <boost/mpl/apply.hpp>
#include <boost/type_traits/is_same.hpp>
#include <boost/xpressive/proto/proto_fwd.hpp>
#include <boost/xpressive/proto/detail/suffix.hpp>
namespace boost { namespace proto { namespace transform
{
template<typename Predicate, typename Grammar0, typename Grammar1>
struct conditional
: Grammar0
{
conditional();
BOOST_MPL_ASSERT((is_same<typename Grammar0::type, typename
Grammar1::type>));
template<typename Expr, typename State, typename Visitor>
struct apply
{
typedef typename mpl::if_<
typename mpl::apply1<Predicate, Expr>::type
, Grammar0
, Grammar1
>::type grammar_type;
typedef typename grammar_type::template apply<Expr, State,
Visitor>::type type;
};
template<typename Expr, typename State, typename Visitor>
static typename apply<Expr, State, Visitor>::type
call(Expr const &expr, State const &state, Visitor &visitor)
{
typedef typename mpl::if_<
typename mpl::apply1<Predicate, Expr>::type
, Grammar0
, Grammar1
>::type grammar_type;
return grammar_type::call(expr, state, visitor);
}
};
}}}
#endif
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