Chris@16: #ifndef BOOST_SERIALIZATION_SMART_CAST_HPP
Chris@16: #define BOOST_SERIALIZATION_SMART_CAST_HPP
Chris@16: 
Chris@16: // MS compatible compilers support #pragma once
Chris@101: #if defined(_MSC_VER)
Chris@16: # pragma once
Chris@16: #endif
Chris@16: 
Chris@16: /////////1/////////2/////////3/////////4/////////5/////////6/////////7/////////8
Chris@16: // smart_cast.hpp:
Chris@16: 
Chris@16: // (C) Copyright 2002 Robert Ramey - http://www.rrsd.com . 
Chris@16: // Use, modification and distribution is subject to the Boost Software
Chris@16: // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
Chris@16: // http://www.boost.org/LICENSE_1_0.txt)
Chris@16: 
Chris@16: //  See http://www.boost.org/libs/serialization for updates, documentation, and revision history.
Chris@16: 
Chris@16: // casting of pointers and references.  
Chris@16: 
Chris@16: // In casting between different C++ classes, there are a number of
Chris@16: // rules that have to be kept in mind in deciding whether to use
Chris@16: // static_cast or dynamic_cast.  
Chris@16: 
Chris@16: // a) dynamic casting can only be applied when one of the types is polymorphic
Chris@16: // Otherwise static_cast must be used.
Chris@16: // b) only dynamic casting can do runtime error checking
Chris@16: // use of static_cast is generally un checked even when compiled for debug
Chris@16: // c) static_cast would be considered faster than dynamic_cast.
Chris@16: 
Chris@16: // If casting is applied to a template parameter, there is no apriori way
Chris@16: // to know which of the two casting methods will be permitted or convenient.
Chris@16: 
Chris@16: // smart_cast uses C++ type_traits, and program debug mode to select the
Chris@16: // most convenient cast to use.
Chris@16: 
Chris@16: #include <exception>
Chris@16: #include <typeinfo>
Chris@16: #include <cstddef> // NULL
Chris@16: 
Chris@16: #include <boost/config.hpp>
Chris@16: #include <boost/static_assert.hpp>
Chris@16: 
Chris@16: #include <boost/type_traits/is_base_and_derived.hpp>
Chris@16: #include <boost/type_traits/is_polymorphic.hpp>
Chris@16: #include <boost/type_traits/is_pointer.hpp>
Chris@16: #include <boost/type_traits/is_reference.hpp>
Chris@16: #include <boost/type_traits/is_same.hpp>
Chris@16: #include <boost/type_traits/remove_pointer.hpp>
Chris@16: #include <boost/type_traits/remove_reference.hpp>
Chris@16: 
Chris@16: #include <boost/mpl/eval_if.hpp>
Chris@16: #include <boost/mpl/if.hpp>
Chris@16: #include <boost/mpl/or.hpp>
Chris@16: #include <boost/mpl/and.hpp>
Chris@16: #include <boost/mpl/not.hpp>
Chris@16: #include <boost/mpl/identity.hpp>
Chris@16: 
Chris@16: #include <boost/serialization/throw_exception.hpp>
Chris@16: 
Chris@16: namespace boost {
Chris@16: namespace serialization {
Chris@16: namespace smart_cast_impl {
Chris@16: 
Chris@16:     template<class T>
Chris@16:     struct reference {
Chris@16: 
Chris@16:         struct polymorphic {
Chris@16: 
Chris@16:             struct linear {
Chris@16:                 template<class U>
Chris@16:                  static T cast(U & u){
Chris@16:                     return static_cast< T >(u);
Chris@16:                 }
Chris@16:             };
Chris@16: 
Chris@16:             struct cross {
Chris@16:                  template<class U>
Chris@16:                 static T cast(U & u){
Chris@16:                     return dynamic_cast< T >(u);
Chris@16:                 }
Chris@16:             };
Chris@16: 
Chris@16:             template<class U>
Chris@16:             static T cast(U & u){
Chris@16:                 // if we're in debug mode
Chris@16:                 #if ! defined(NDEBUG)                               \
Chris@16:                 || defined(__BORLANDC__) && (__BORLANDC__ <= 0x560) \
Chris@16:                 || defined(__MWERKS__)
Chris@16:                     // do a checked dynamic cast
Chris@16:                     return cross::cast(u);
Chris@16:                 #else
Chris@16:                     // borland 5.51 chokes here so we can't use it
Chris@16:                     // note: if remove_reference isn't function for these types
Chris@16:                     // cross casting will be selected this will work but will
Chris@16:                     // not be the most efficient method. This will conflict with
Chris@16:                     // the original smart_cast motivation.
Chris@101:                     typedef typename mpl::eval_if<
Chris@101:                             typename mpl::and_<
Chris@16:                                 mpl::not_<is_base_and_derived<
Chris@101:                                     typename remove_reference< T >::type,
Chris@16:                                     U
Chris@16:                                 > >,
Chris@16:                                 mpl::not_<is_base_and_derived<
Chris@16:                                     U,
Chris@101:                                     typename remove_reference< T >::type
Chris@16:                                 > >
Chris@16:                             >,
Chris@16:                             // borland chokes w/o full qualification here
Chris@16:                             mpl::identity<cross>,
Chris@16:                             mpl::identity<linear>
Chris@16:                     >::type typex;
Chris@16:                     // typex works around gcc 2.95 issue
Chris@16:                     return typex::cast(u);
Chris@16:                 #endif
Chris@16:             }
Chris@16:         };
Chris@16: 
Chris@16:         struct non_polymorphic {
Chris@16:             template<class U>
Chris@16:              static T cast(U & u){
Chris@16:                 return static_cast< T >(u);
Chris@16:             }
Chris@16:         };
Chris@16:         template<class U>
Chris@16:         static T cast(U & u){
Chris@16:             #if defined(__BORLANDC__)
Chris@16:                 return mpl::eval_if<
Chris@16:                     boost::is_polymorphic<U>,
Chris@16:                     mpl::identity<polymorphic>,
Chris@16:                     mpl::identity<non_polymorphic>
Chris@16:                 >::type::cast(u);
Chris@16:             #else
Chris@101:                 typedef typename mpl::eval_if<
Chris@16:                     boost::is_polymorphic<U>,
Chris@16:                     mpl::identity<polymorphic>,
Chris@16:                     mpl::identity<non_polymorphic>
Chris@16:                 >::type typex;
Chris@16:                 return typex::cast(u);
Chris@16:             #endif
Chris@16:         }
Chris@16:     };
Chris@16: 
Chris@16:     template<class T>
Chris@16:     struct pointer {
Chris@16: 
Chris@16:         struct polymorphic {
Chris@16:             // unfortunately, this below fails to work for virtual base 
Chris@16:             // classes.  need has_virtual_base to do this.
Chris@16:             // Subject for further study
Chris@16:             #if 0
Chris@16:             struct linear {
Chris@16:                 template<class U>
Chris@16:                  static T cast(U * u){
Chris@16:                     return static_cast< T >(u);
Chris@16:                 }
Chris@16:             };
Chris@16: 
Chris@16:             struct cross {
Chris@16:                 template<class U>
Chris@16:                 static T cast(U * u){
Chris@16:                     T tmp = dynamic_cast< T >(u);
Chris@16:                     #ifndef NDEBUG
Chris@16:                         if ( tmp == 0 ) throw_exception(std::bad_cast());
Chris@16:                     #endif
Chris@16:                     return tmp;
Chris@16:                 }
Chris@16:             };
Chris@16: 
Chris@16:             template<class U>
Chris@16:             static T cast(U * u){
Chris@16:                 // if we're in debug mode
Chris@101:                 #if 0 //! defined(NDEBUG) || defined(__BORLANDC__) && (__BORLANDC__ <= 0x560)
Chris@16:                     // do a checked dynamic cast
Chris@16:                     return cross::cast(u);
Chris@16:                 #else
Chris@16:                     // borland 5.51 chokes here so we can't use it
Chris@16:                     // note: if remove_pointer isn't function for these types
Chris@16:                     // cross casting will be selected this will work but will
Chris@16:                     // not be the most efficient method. This will conflict with
Chris@16:                     // the original smart_cast motivation.
Chris@16:                     typedef
Chris@101:                         typename mpl::eval_if<
Chris@101:                             typename mpl::and_<
Chris@16:                                 mpl::not_<is_base_and_derived<
Chris@101:                                     typename remove_pointer< T >::type,
Chris@16:                                     U
Chris@16:                                 > >,
Chris@16:                                 mpl::not_<is_base_and_derived<
Chris@16:                                     U,
Chris@101:                                     typename remove_pointer< T >::type
Chris@16:                                 > >
Chris@16:                             >,
Chris@16:                             // borland chokes w/o full qualification here
Chris@16:                             mpl::identity<cross>,
Chris@16:                             mpl::identity<linear>
Chris@16:                         >::type typex;
Chris@16:                     return typex::cast(u);
Chris@16:                 #endif
Chris@16:             }
Chris@16:             #else
Chris@16:             template<class U>
Chris@16:             static T cast(U * u){
Chris@16:                 T tmp = dynamic_cast< T >(u);
Chris@16:                 #ifndef NDEBUG
Chris@16:                     if ( tmp == 0 ) throw_exception(std::bad_cast());
Chris@16:                 #endif
Chris@16:                 return tmp;
Chris@16:             }
Chris@16:             #endif
Chris@16:         };
Chris@16: 
Chris@16:         struct non_polymorphic {
Chris@16:             template<class U>
Chris@16:              static T cast(U * u){
Chris@16:                 return static_cast< T >(u);
Chris@16:             }
Chris@16:         };
Chris@16: 
Chris@16:         template<class U>
Chris@16:         static T cast(U * u){
Chris@16:             #if defined(__BORLANDC__)
Chris@16:                 return mpl::eval_if<
Chris@16:                     boost::is_polymorphic<U>,
Chris@16:                     mpl::identity<polymorphic>,
Chris@16:                     mpl::identity<non_polymorphic>
Chris@16:                 >::type::cast(u);
Chris@16:             #else
Chris@101:                 typedef typename mpl::eval_if<
Chris@16:                     boost::is_polymorphic<U>,
Chris@16:                     mpl::identity<polymorphic>,
Chris@16:                     mpl::identity<non_polymorphic>
Chris@16:                 >::type typex;
Chris@16:                 return typex::cast(u);
Chris@16:             #endif
Chris@16:         }
Chris@16: 
Chris@16:     };
Chris@16: 
Chris@16:     template<class TPtr>
Chris@16:     struct void_pointer {
Chris@16:         template<class UPtr>
Chris@16:         static TPtr cast(UPtr uptr){
Chris@16:             return static_cast<TPtr>(uptr);
Chris@16:         }
Chris@16:     };
Chris@16: 
Chris@16:     template<class T>
Chris@16:     struct error {
Chris@16:         // if we get here, its because we are using one argument in the
Chris@16:         // cast on a system which doesn't support partial template 
Chris@16:         // specialization
Chris@16:         template<class U>
Chris@16:         static T cast(U u){
Chris@16:             BOOST_STATIC_ASSERT(sizeof(T)==0);
Chris@16:             return * static_cast<T *>(NULL);
Chris@16:         }
Chris@16:     };
Chris@16: 
Chris@16: } // smart_cast_impl
Chris@16: 
Chris@16: // this implements:
Chris@16: // smart_cast<Target *, Source *>(Source * s)
Chris@16: // smart_cast<Target &, Source &>(s)
Chris@16: // note that it will fail with
Chris@16: // smart_cast<Target &>(s)
Chris@16: template<class T, class U>
Chris@16: T smart_cast(U u) {
Chris@16:     typedef
Chris@101:         typename mpl::eval_if<
Chris@101:             typename mpl::or_<
Chris@16:                 boost::is_same<void *, U>,
Chris@16:                 boost::is_same<void *, T>,
Chris@16:                 boost::is_same<const void *, U>,
Chris@16:                 boost::is_same<const void *, T>
Chris@16:             >,
Chris@16:             mpl::identity<smart_cast_impl::void_pointer< T > >,
Chris@16:         // else
Chris@101:         typename mpl::eval_if<boost::is_pointer<U>,
Chris@16:             mpl::identity<smart_cast_impl::pointer< T > >,
Chris@16:         // else
Chris@101:         typename mpl::eval_if<boost::is_reference<U>,
Chris@16:             mpl::identity<smart_cast_impl::reference< T > >,
Chris@16:         // else
Chris@16:             mpl::identity<smart_cast_impl::error< T >
Chris@16:         >
Chris@16:         >
Chris@16:         >
Chris@16:         >::type typex;
Chris@16:     return typex::cast(u);
Chris@16: }
Chris@16: 
Chris@16: // this implements:
Chris@16: // smart_cast_reference<Target &>(Source & s)
Chris@16: template<class T, class U>
Chris@16: T smart_cast_reference(U & u) {
Chris@16:     return smart_cast_impl::reference< T >::cast(u);
Chris@16: }
Chris@16: 
Chris@16: } // namespace serialization
Chris@16: } // namespace boost
Chris@16: 
Chris@16: #endif // BOOST_SERIALIZATION_SMART_CAST_HPP