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276 lines
8.7 KiB
C++
276 lines
8.7 KiB
C++
#ifndef BOOST_SERIALIZATION_SMART_CAST_HPP
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#define BOOST_SERIALIZATION_SMART_CAST_HPP
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// MS compatible compilers support #pragma once
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#if defined(_MSC_VER)
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# pragma once
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#endif
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/////////1/////////2/////////3/////////4/////////5/////////6/////////7/////////8
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// smart_cast.hpp:
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// (C) Copyright 2002 Robert Ramey - http://www.rrsd.com .
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// Use, modification and distribution is subject to the Boost Software
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// License, Version 1.0. (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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// See http://www.boost.org/libs/serialization for updates, documentation, and revision history.
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// casting of pointers and references.
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// In casting between different C++ classes, there are a number of
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// rules that have to be kept in mind in deciding whether to use
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// static_cast or dynamic_cast.
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// a) dynamic casting can only be applied when one of the types is polymorphic
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// Otherwise static_cast must be used.
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// b) only dynamic casting can do runtime error checking
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// use of static_cast is generally un checked even when compiled for debug
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// c) static_cast would be considered faster than dynamic_cast.
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// If casting is applied to a template parameter, there is no apriori way
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// to know which of the two casting methods will be permitted or convenient.
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// smart_cast uses C++ type_traits, and program debug mode to select the
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// most convenient cast to use.
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#include <exception>
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#include <typeinfo>
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#include <cstddef> // NULL
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#include <boost/config.hpp>
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#include <boost/static_assert.hpp>
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#include <boost/type_traits/is_base_and_derived.hpp>
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#include <boost/type_traits/is_polymorphic.hpp>
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#include <boost/type_traits/is_pointer.hpp>
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#include <boost/type_traits/is_reference.hpp>
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#include <boost/type_traits/is_same.hpp>
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#include <boost/type_traits/remove_pointer.hpp>
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#include <boost/type_traits/remove_reference.hpp>
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#include <boost/mpl/eval_if.hpp>
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#include <boost/mpl/if.hpp>
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#include <boost/mpl/or.hpp>
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#include <boost/mpl/and.hpp>
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#include <boost/mpl/not.hpp>
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#include <boost/mpl/identity.hpp>
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#include <boost/serialization/throw_exception.hpp>
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namespace boost {
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namespace serialization {
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namespace smart_cast_impl {
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template<class T>
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struct reference {
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struct polymorphic {
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struct linear {
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template<class U>
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static T cast(U & u){
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return static_cast< T >(u);
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}
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};
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struct cross {
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template<class U>
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static T cast(U & u){
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return dynamic_cast< T >(u);
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}
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};
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template<class U>
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static T cast(U & u){
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// if we're in debug mode
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#if ! defined(NDEBUG) \
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|| defined(__MWERKS__)
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// do a checked dynamic cast
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return cross::cast(u);
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#else
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// borland 5.51 chokes here so we can't use it
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// note: if remove_reference isn't function for these types
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// cross casting will be selected this will work but will
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// not be the most efficient method. This will conflict with
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// the original smart_cast motivation.
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typedef typename mpl::eval_if<
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typename mpl::and_<
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mpl::not_<is_base_and_derived<
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typename remove_reference< T >::type,
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U
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> >,
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mpl::not_<is_base_and_derived<
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U,
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typename remove_reference< T >::type
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> >
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>,
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// borland chokes w/o full qualification here
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mpl::identity<cross>,
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mpl::identity<linear>
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>::type typex;
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// typex works around gcc 2.95 issue
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return typex::cast(u);
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#endif
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}
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};
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struct non_polymorphic {
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template<class U>
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static T cast(U & u){
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return static_cast< T >(u);
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}
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};
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template<class U>
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static T cast(U & u){
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typedef typename mpl::eval_if<
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boost::is_polymorphic<U>,
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mpl::identity<polymorphic>,
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mpl::identity<non_polymorphic>
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>::type typex;
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return typex::cast(u);
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}
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};
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template<class T>
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struct pointer {
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struct polymorphic {
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// unfortunately, this below fails to work for virtual base
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// classes. need has_virtual_base to do this.
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// Subject for further study
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#if 0
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struct linear {
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template<class U>
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static T cast(U * u){
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return static_cast< T >(u);
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}
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};
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struct cross {
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template<class U>
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static T cast(U * u){
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T tmp = dynamic_cast< T >(u);
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#ifndef NDEBUG
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if ( tmp == 0 ) throw_exception(std::bad_cast());
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#endif
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return tmp;
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}
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};
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template<class U>
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static T cast(U * u){
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typedef
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typename mpl::eval_if<
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typename mpl::and_<
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mpl::not_<is_base_and_derived<
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typename remove_pointer< T >::type,
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U
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> >,
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mpl::not_<is_base_and_derived<
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U,
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typename remove_pointer< T >::type
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> >
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>,
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// borland chokes w/o full qualification here
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mpl::identity<cross>,
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mpl::identity<linear>
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>::type typex;
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return typex::cast(u);
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}
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#else
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template<class U>
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static T cast(U * u){
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T tmp = dynamic_cast< T >(u);
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#ifndef NDEBUG
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if ( tmp == 0 ) throw_exception(std::bad_cast());
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#endif
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return tmp;
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}
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#endif
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};
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struct non_polymorphic {
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template<class U>
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static T cast(U * u){
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return static_cast< T >(u);
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}
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};
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template<class U>
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static T cast(U * u){
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typedef typename mpl::eval_if<
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boost::is_polymorphic<U>,
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mpl::identity<polymorphic>,
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mpl::identity<non_polymorphic>
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>::type typex;
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return typex::cast(u);
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}
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};
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template<class TPtr>
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struct void_pointer {
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template<class UPtr>
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static TPtr cast(UPtr uptr){
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return static_cast<TPtr>(uptr);
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}
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};
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template<class T>
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struct error {
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// if we get here, its because we are using one argument in the
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// cast on a system which doesn't support partial template
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// specialization
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template<class U>
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static T cast(U){
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BOOST_STATIC_ASSERT(sizeof(T)==0);
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return * static_cast<T *>(NULL);
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}
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};
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} // smart_cast_impl
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// this implements:
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// smart_cast<Target *, Source *>(Source * s)
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// smart_cast<Target &, Source &>(s)
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// note that it will fail with
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// smart_cast<Target &>(s)
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template<class T, class U>
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T smart_cast(U u) {
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typedef
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typename mpl::eval_if<
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typename mpl::or_<
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boost::is_same<void *, U>,
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boost::is_same<void *, T>,
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boost::is_same<const void *, U>,
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boost::is_same<const void *, T>
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>,
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mpl::identity<smart_cast_impl::void_pointer< T > >,
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// else
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typename mpl::eval_if<boost::is_pointer<U>,
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mpl::identity<smart_cast_impl::pointer< T > >,
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// else
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typename mpl::eval_if<boost::is_reference<U>,
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mpl::identity<smart_cast_impl::reference< T > >,
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// else
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mpl::identity<smart_cast_impl::error< T >
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>
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>
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>
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>::type typex;
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return typex::cast(u);
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}
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// this implements:
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// smart_cast_reference<Target &>(Source & s)
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template<class T, class U>
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T smart_cast_reference(U & u) {
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return smart_cast_impl::reference< T >::cast(u);
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}
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} // namespace serialization
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} // namespace boost
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#endif // BOOST_SERIALIZATION_SMART_CAST_HPP
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