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147 lines
3.3 KiB
147 lines
3.3 KiB
/* Copyright 2003-2008 Joaquin M Lopez Munoz. |
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* Distributed under the Boost Software License, Version 1.0. |
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* (See accompanying file LICENSE_1_0.txt or copy at |
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* http://www.boost.org/LICENSE_1_0.txt) |
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* |
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* See http://www.boost.org/libs/multi_index for library home page. |
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*/ |
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#ifndef BOOST_MULTI_INDEX_IDENTITY_HPP |
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#define BOOST_MULTI_INDEX_IDENTITY_HPP |
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#if defined(_MSC_VER)&&(_MSC_VER>=1200) |
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#pragma once |
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#endif |
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#include <boost/config.hpp> |
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#include <boost/mpl/if.hpp> |
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#include <boost/multi_index/identity_fwd.hpp> |
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#include <boost/type_traits/is_const.hpp> |
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#include <boost/type_traits/remove_const.hpp> |
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#include <boost/utility/enable_if.hpp> |
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#if !defined(BOOST_NO_SFINAE) |
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#include <boost/type_traits/is_convertible.hpp> |
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#endif |
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namespace boost{ |
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template<class Type> class reference_wrapper; /* fwd decl. */ |
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namespace multi_index{ |
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namespace detail{ |
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/* identity is a do-nothing key extractor that returns the [const] Type& |
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* object passed. |
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* Additionally, identity is overloaded to support referece_wrappers |
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* of Type and "chained pointers" to Type's. By chained pointer to Type we |
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* mean a type P such that, given a p of type P |
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* *...n...*x is convertible to Type&, for some n>=1. |
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* Examples of chained pointers are raw and smart pointers, iterators and |
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* arbitrary combinations of these (vg. Type** or auto_ptr<Type*>.) |
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*/ |
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/* NB. Some overloads of operator() have an extra dummy parameter int=0. |
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* This disambiguator serves several purposes: |
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* - Without it, MSVC++ 6.0 incorrectly regards some overloads as |
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* specializations of a previous member function template. |
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* - MSVC++ 6.0/7.0 seem to incorrectly treat some different memfuns |
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* as if they have the same signature. |
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* - If remove_const is broken due to lack of PTS, int=0 avoids the |
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* declaration of memfuns with identical signature. |
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*/ |
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template<typename Type> |
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struct const_identity_base |
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{ |
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typedef Type result_type; |
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template<typename ChainedPtr> |
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#if !defined(BOOST_NO_SFINAE) |
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typename disable_if<is_convertible<const ChainedPtr&,Type&>,Type&>::type |
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#else |
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Type& |
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#endif |
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operator()(const ChainedPtr& x)const |
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{ |
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return operator()(*x); |
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} |
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Type& operator()(Type& x)const |
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{ |
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return x; |
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} |
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Type& operator()(const reference_wrapper<Type>& x)const |
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{ |
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return x.get(); |
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} |
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Type& operator()( |
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const reference_wrapper<typename remove_const<Type>::type>& x,int=0)const |
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{ |
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return x.get(); |
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} |
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}; |
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template<typename Type> |
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struct non_const_identity_base |
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{ |
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typedef Type result_type; |
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/* templatized for pointer-like types */ |
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template<typename ChainedPtr> |
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#if !defined(BOOST_NO_SFINAE) |
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typename disable_if< |
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is_convertible<const ChainedPtr&,const Type&>,Type&>::type |
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#else |
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Type& |
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#endif |
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operator()(const ChainedPtr& x)const |
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{ |
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return operator()(*x); |
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} |
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const Type& operator()(const Type& x,int=0)const |
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{ |
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return x; |
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} |
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Type& operator()(Type& x)const |
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{ |
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return x; |
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} |
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const Type& operator()(const reference_wrapper<const Type>& x,int=0)const |
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{ |
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return x.get(); |
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} |
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Type& operator()(const reference_wrapper<Type>& x)const |
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{ |
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return x.get(); |
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} |
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}; |
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} /* namespace multi_index::detail */ |
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template<class Type> |
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struct identity: |
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mpl::if_c< |
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is_const<Type>::value, |
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detail::const_identity_base<Type>,detail::non_const_identity_base<Type> |
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>::type |
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{ |
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}; |
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} /* namespace multi_index */ |
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} /* namespace boost */ |
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#endif
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