/* Copyright 2003-2006 Joaquín M López Muñoz.

  * 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)&&(_MSC_VER>=1200)

 #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*>.)

  */

 /* NB. Some overloads of operator() have an extra dummy parameter int=0.

  * This disambiguator serves several purposes:

  *  - Without it, MSVC++ 6.0 incorrectly regards some overloads as

  *    specializations of a previous member function template.

  *  - MSVC++ 6.0/7.0 seem to incorrectly treat some different memfuns

  *    as if they have the same signature.

  *  - If remove_const is broken due to lack of PTS, int=0 avoids the

  *    declaration of memfuns with identical signature.

  */

 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,int=0)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,int=0)const

   {

     return x;

   }

   Type& operator()(Type& x)const

   {

     return x;

   }

   const Type& operator()(const reference_wrapper<const Type>& x,int=0)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