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/* Copyright 2003-2013 Joaquin M Lopez Munoz.
* 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)
*
* See http://www.boost.org/libs/multi_index for library home page.
*/
#ifndef BOOST_MULTI_INDEX_IDENTITY_HPP
#define BOOST_MULTI_INDEX_IDENTITY_HPP
#if defined(_MSC_VER)
#pragma once
#endif
#include <boost/config.hpp>
#include <boost/mpl/if.hpp>
#include <boost/multi_index/identity_fwd.hpp>
#include <boost/type_traits/is_const.hpp>
#include <boost/type_traits/remove_const.hpp>
#include <boost/utility/enable_if.hpp>
#if !defined(BOOST_NO_SFINAE)
#include <boost/type_traits/is_convertible.hpp>
#endif
namespace boost{
template<class Type> class reference_wrapper; /* fwd decl. */
namespace multi_index{
namespace detail{
/* identity is a do-nothing key extractor that returns the [const] Type&
* object passed.
* Additionally, identity is overloaded to support referece_wrappers
* of Type and "chained pointers" to Type's. By chained pointer to Type we
* mean a type P such that, given a p of type P
* *...n...*x is convertible to Type&, for some n>=1.
* Examples of chained pointers are raw and smart pointers, iterators and
* arbitrary combinations of these (vg. Type** or auto_ptr<Type*>.)
*/
template<typename Type>
struct const_identity_base
{
typedef Type result_type;
template<typename ChainedPtr>
#if !defined(BOOST_NO_SFINAE)
typename disable_if<is_convertible<const ChainedPtr&,Type&>,Type&>::type
#else
Type&
#endif
operator()(const ChainedPtr& x)const
{
return operator()(*x);
}
Type& operator()(Type& x)const
{
return x;
}
Type& operator()(const reference_wrapper<Type>& x)const
{
return x.get();
}
Type& operator()(
const reference_wrapper<typename remove_const<Type>::type>& x)const
{
return x.get();
}
};
template<typename Type>
struct non_const_identity_base
{
typedef Type result_type;
/* templatized for pointer-like types */
template<typename ChainedPtr>
#if !defined(BOOST_NO_SFINAE)
typename disable_if<
is_convertible<const ChainedPtr&,const Type&>,Type&>::type
#else
Type&
#endif
operator()(const ChainedPtr& x)const
{
return operator()(*x);
}
const Type& operator()(const Type& x)const
{
return x;
}
Type& operator()(Type& x)const
{
return x;
}
const Type& operator()(const reference_wrapper<const Type>& x)const
{
return x.get();
}
Type& operator()(const reference_wrapper<Type>& x)const
{
return x.get();
}
};
} /* namespace multi_index::detail */
template<class Type>
struct identity:
mpl::if_c<
is_const<Type>::value,
detail::const_identity_base<Type>,detail::non_const_identity_base<Type>
>::type
{
};
} /* namespace multi_index */
} /* namespace boost */
#endif
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