boost/spirit/home/x3/support/traits/make_attribute.hpp
/*=============================================================================
Copyright (c) 2001-2014 Joel de Guzman
Copyright (c) 2001-2012 Hartmut Kaiser
http://spirit.sourceforge.net/
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)
=============================================================================*/
#if !defined(BOOST_SPIRIT_X3_MAKE_ATTRIBUTE_JAN_8_2012_0721PM)
#define BOOST_SPIRIT_X3_MAKE_ATTRIBUTE_JAN_8_2012_0721PM
#include <boost/mpl/if.hpp>
#include <boost/type_traits/remove_const.hpp>
#include <boost/type_traits/add_reference.hpp>
#include <boost/spirit/home/x3/support/unused.hpp>
namespace boost { namespace spirit { namespace x3 { namespace traits
{
template <typename Attribute>
struct make_attribute_base
{
static Attribute call(unused_type)
{
// synthesize the attribute/parameter
return Attribute();
}
template <typename T>
static T& call(T& value)
{
return value; // just pass the one provided
}
};
template <typename Attribute, typename ActualAttribute>
struct make_attribute : make_attribute_base<Attribute>
{
typedef ActualAttribute& type;
typedef ActualAttribute value_type;
};
template <typename Attribute>
struct make_attribute<Attribute, unused_type>
: make_attribute_base<Attribute>
{
typedef typename remove_const<Attribute>::type attribute_type;
typedef attribute_type type;
typedef attribute_type value_type;
};
template <typename Attribute, typename ActualAttribute>
struct make_attribute<Attribute&, ActualAttribute>
: make_attribute<Attribute, ActualAttribute> {};
template <typename Attribute, typename ActualAttribute>
struct make_attribute<Attribute const&, ActualAttribute>
: make_attribute<Attribute const, ActualAttribute> {};
template <typename ActualAttribute>
struct make_attribute<unused_type, ActualAttribute>
{
typedef unused_type type;
typedef unused_type value_type;
static unused_type call(unused_type)
{
return unused;
}
};
template <>
struct make_attribute<unused_type, unused_type>
{
typedef unused_type type;
typedef unused_type value_type;
static unused_type call(unused_type)
{
return unused;
}
};
}}}}
#endif
