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/* Copyright 2003-2015 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/detail/workaround.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 unique_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 #if BOOST_WORKAROUND(BOOST_MSVC,==1310) /* http://lists.boost.org/Archives/boost/2015/10/226135.php */ ,int=0 #endif )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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