148 lines
3.3 KiB
C++
148 lines
3.3 KiB
C++
/* 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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