williamr@2: #ifndef BOOST_SMART_CAST_HPP
williamr@2: #define BOOST_SMART_CAST_HPP
williamr@2: 
williamr@2: // MS compatible compilers support #pragma once
williamr@2: #if defined(_MSC_VER) && (_MSC_VER >= 1020)
williamr@2: # pragma once
williamr@2: #endif
williamr@2: 
williamr@2: /////////1/////////2/////////3/////////4/////////5/////////6/////////7/////////8
williamr@2: // smart_cast.hpp:
williamr@2: 
williamr@2: // (C) Copyright 2002 Robert Ramey - http://www.rrsd.com . 
williamr@2: // Use, modification and distribution is subject to the Boost Software
williamr@2: // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
williamr@2: // http://www.boost.org/LICENSE_1_0.txt)
williamr@2: 
williamr@2: //  See http://www.boost.org for updates, documentation, and revision history.
williamr@2: 
williamr@2: // casting of pointers and references.  
williamr@2: 
williamr@2: // In casting between different C++ classes, there are a number of
williamr@2: // rules that have to be kept in mind in deciding whether to use
williamr@2: // static_cast or dynamic_cast.  
williamr@2: 
williamr@2: // a) dynamic casting can only be applied when one of the types is polymorphic
williamr@2: // Otherwise static_cast must be used.
williamr@2: // b) only dynamic casting can do runtime error checking
williamr@2: // use of static_cast is generally un checked even when compiled for debug
williamr@2: // c) static_cast would be considered faster than dynamic_cast.
williamr@2: 
williamr@2: // If casting is applied to a template parameter, there is no apriori way
williamr@2: // to know which of the two casting methods will be permitted or convenient.
williamr@2: 
williamr@2: // smart_cast uses C++ type_traits, and program debug mode to select the
williamr@2: // most convenient cast to use.
williamr@2: 
williamr@2: #include <exception>
williamr@2: #include <typeinfo>
williamr@2: 
williamr@2: #include <boost/config.hpp>
williamr@2: #include <boost/static_assert.hpp>
williamr@2: 
williamr@2: #include <boost/type_traits/is_base_and_derived.hpp>
williamr@2: #include <boost/type_traits/is_polymorphic.hpp>
williamr@2: #include <boost/type_traits/is_pointer.hpp>
williamr@2: #include <boost/type_traits/is_reference.hpp>
williamr@2: #include <boost/type_traits/is_same.hpp>
williamr@2: #include <boost/type_traits/remove_pointer.hpp>
williamr@2: #include <boost/type_traits/remove_reference.hpp>
williamr@2: 
williamr@2: #include <boost/mpl/eval_if.hpp>
williamr@2: #include <boost/mpl/if.hpp>
williamr@2: #include <boost/mpl/or.hpp>
williamr@2: #include <boost/mpl/and.hpp>
williamr@2: #include <boost/mpl/not.hpp>
williamr@2: #include <boost/mpl/identity.hpp>
williamr@2: 
williamr@2: namespace boost {
williamr@2: namespace smart_cast_impl {
williamr@2: 
williamr@2:     template<class T>
williamr@2:     struct reference {
williamr@2: 
williamr@2:         struct polymorphic {
williamr@2: 
williamr@2:             struct linear {
williamr@2:                 template<class U>
williamr@2:                  static T cast(U & u){
williamr@2:                     return static_cast<T>(u);
williamr@2:                 }
williamr@2:             };
williamr@2: 
williamr@2:             struct cross {
williamr@2:                  template<class U>
williamr@2:                 static T cast(U & u){
williamr@2:                     return dynamic_cast<T>(u);
williamr@2:                 }
williamr@2:             };
williamr@2: 
williamr@2:             template<class U>
williamr@2:             static T cast(U & u){
williamr@2:                 // if we're in debug mode
williamr@2:                 #if ! defined(NDEBUG)                               \
williamr@2:                 || defined(__BORLANDC__) && (__BORLANDC__ <= 0x560) \
williamr@2:                 || defined(__MWERKS__)
williamr@2:                     // do a checked dynamic cast
williamr@2:                     return cross::cast(u);
williamr@2:                 #else
williamr@2:                     // borland 5.51 chokes here so we can't use it
williamr@2:                     // note: if remove_reference isn't function for these types
williamr@2:                     // cross casting will be selected this will work but will
williamr@2:                     // not be the most efficient method. This will conflict with
williamr@2:                     // the original smart_cast motivation.
williamr@2:                     typedef BOOST_DEDUCED_TYPENAME mpl::eval_if<
williamr@2:                             BOOST_DEDUCED_TYPENAME mpl::and_<
williamr@2:                                 mpl::not_<is_base_and_derived<
williamr@2:                                     BOOST_DEDUCED_TYPENAME remove_reference<T>::type,
williamr@2:                                     U
williamr@2:                                 > >,
williamr@2:                                 mpl::not_<is_base_and_derived<
williamr@2:                                     U,
williamr@2:                                     BOOST_DEDUCED_TYPENAME remove_reference<T>::type
williamr@2:                                 > >
williamr@2:                             >,
williamr@2:                             // borland chokes w/o full qualification here
williamr@2:                             mpl::identity<cross>,
williamr@2:                             mpl::identity<linear>
williamr@2:                     >::type typex;
williamr@2:                     // typex works around gcc 2.95 issue
williamr@2:                     return typex::cast(u);
williamr@2:                 #endif
williamr@2:             }
williamr@2:         };
williamr@2: 
williamr@2:         struct non_polymorphic {
williamr@2:             template<class U>
williamr@2:              static T cast(U & u){
williamr@2:                 return static_cast<T>(u);
williamr@2:             }
williamr@2:         };
williamr@2:         template<class U>
williamr@2:         static T cast(U & u){
williamr@2:             #if defined(__BORLANDC__)
williamr@2:                 return mpl::eval_if<
williamr@2:                     boost::is_polymorphic<U>,
williamr@2:                     mpl::identity<polymorphic>,
williamr@2:                     mpl::identity<non_polymorphic>
williamr@2:                 >::type::cast(u);
williamr@2:             #else
williamr@2:                 typedef BOOST_DEDUCED_TYPENAME mpl::eval_if<
williamr@2:                     boost::is_polymorphic<U>,
williamr@2:                     mpl::identity<polymorphic>,
williamr@2:                     mpl::identity<non_polymorphic>
williamr@2:                 >::type typex;
williamr@2:                 return typex::cast(u);
williamr@2:             #endif
williamr@2:         }
williamr@2:     };
williamr@2: 
williamr@2:     template<class T>
williamr@2:     struct pointer {
williamr@2: 
williamr@2:         struct polymorphic {
williamr@2:             // unfortunately, this below fails to work for virtual base 
williamr@2:             // classes.  need has_virtual_base to do this.
williamr@2:             // Subject for further study
williamr@2:             #if 0
williamr@2:             struct linear {
williamr@2:                 template<class U>
williamr@2:                  static T cast(U * u){
williamr@2:                     return static_cast<T>(u);
williamr@2:                 }
williamr@2:             };
williamr@2: 
williamr@2:             struct cross {
williamr@2:                 template<class U>
williamr@2:                 static T cast(U * u){
williamr@2:                     T tmp = dynamic_cast<T>(u);
williamr@2:                     #ifndef NDEBUG
williamr@2:                         if ( tmp == 0 ) throw std::bad_cast();
williamr@2:                     #endif
williamr@2:                     return tmp;
williamr@2:                 }
williamr@2:             };
williamr@2: 
williamr@2:             template<class U>
williamr@2:             static T cast(U * u){
williamr@2:                 // if we're in debug mode
williamr@2:                 #if ! defined(NDEBUG) || defined(__BORLANDC__) && (__BORLANDC__ <= 0x560)
williamr@2:                     // do a checked dynamic cast
williamr@2:                     return cross::cast(u);
williamr@2:                 #else
williamr@2:                     // borland 5.51 chokes here so we can't use it
williamr@2:                     // note: if remove_pointer isn't function for these types
williamr@2:                     // cross casting will be selected this will work but will
williamr@2:                     // not be the most efficient method. This will conflict with
williamr@2:                     // the original smart_cast motivation.
williamr@2:                     typedef
williamr@2:                         BOOST_DEDUCED_TYPENAME mpl::eval_if<
williamr@2:                             BOOST_DEDUCED_TYPENAME mpl::and_<
williamr@2:                                 mpl::not_<is_base_and_derived<
williamr@2:                                     BOOST_DEDUCED_TYPENAME remove_pointer<T>::type,
williamr@2:                                     U
williamr@2:                                 > >,
williamr@2:                                 mpl::not_<is_base_and_derived<
williamr@2:                                     U,
williamr@2:                                     BOOST_DEDUCED_TYPENAME remove_pointer<T>::type
williamr@2:                                 > >
williamr@2:                             >,
williamr@2:                             // borland chokes w/o full qualification here
williamr@2:                             mpl::identity<cross>,
williamr@2:                             mpl::identity<linear>
williamr@2:                         >::type typex;
williamr@2:                     return typex::cast(u);
williamr@2:                 #endif
williamr@2:             }
williamr@2:             #else
williamr@2:             template<class U>
williamr@2:             static T cast(U * u){
williamr@2:                 T tmp = dynamic_cast<T>(u);
williamr@2:                 #ifndef NDEBUG
williamr@2:                     if ( tmp == 0 ) throw std::bad_cast();
williamr@2:                 #endif
williamr@2:                 return tmp;
williamr@2:             }
williamr@2:             #endif
williamr@2:         };
williamr@2: 
williamr@2:         struct non_polymorphic {
williamr@2:             template<class U>
williamr@2:              static T cast(U * u){
williamr@2:                 return static_cast<T>(u);
williamr@2:             }
williamr@2:         };
williamr@2: 
williamr@2:         template<class U>
williamr@2:         static T cast(U * u){
williamr@2:             #if defined(__BORLANDC__)
williamr@2:                 return mpl::eval_if<
williamr@2:                     boost::is_polymorphic<U>,
williamr@2:                     mpl::identity<polymorphic>,
williamr@2:                     mpl::identity<non_polymorphic>
williamr@2:                 >::type::cast(u);
williamr@2:             #else
williamr@2:                 typedef BOOST_DEDUCED_TYPENAME mpl::eval_if<
williamr@2:                     boost::is_polymorphic<U>,
williamr@2:                     mpl::identity<polymorphic>,
williamr@2:                     mpl::identity<non_polymorphic>
williamr@2:                 >::type typex;
williamr@2:                 return typex::cast(u);
williamr@2:             #endif
williamr@2:         }
williamr@2: 
williamr@2:     };
williamr@2: 
williamr@2:     template<class TPtr>
williamr@2:     struct void_pointer {
williamr@2:         template<class UPtr>
williamr@2:         static TPtr cast(UPtr uptr){
williamr@2:             return static_cast<TPtr>(uptr);
williamr@2:         }
williamr@2:     };
williamr@2: 
williamr@2:     template<class T>
williamr@2:     struct error {
williamr@2:         // if we get here, its because we are using one argument in the
williamr@2:         // cast on a system which doesn't support partial template 
williamr@2:         // specialization
williamr@2:         template<class U>
williamr@2:         static T cast(U u){
williamr@2:             BOOST_STATIC_ASSERT(sizeof(T)==0);
williamr@2:             return * static_cast<T *>(NULL);
williamr@2:         }
williamr@2:     };
williamr@2: 
williamr@2: } // smart_cast_impl
williamr@2: 
williamr@2: // this implements:
williamr@2: // smart_cast<Target *, Source *>(Source * s)
williamr@2: // smart_cast<Target &, Source &>(s)
williamr@2: // note that it will fail with
williamr@2: // smart_cast<Target &>(s)
williamr@2: template<class T, class U>
williamr@2: T smart_cast(U u) {
williamr@2:     typedef
williamr@2:         BOOST_DEDUCED_TYPENAME mpl::eval_if<
williamr@2:             BOOST_DEDUCED_TYPENAME mpl::or_<
williamr@2:                 boost::is_same<void *, U>,
williamr@2:                 boost::is_same<void *, T>,
williamr@2:                 boost::is_same<const void *, U>,
williamr@2:                 boost::is_same<const void *, T>
williamr@2:             >,
williamr@2:             mpl::identity<smart_cast_impl::void_pointer<T> >,
williamr@2:         // else
williamr@2:         BOOST_DEDUCED_TYPENAME mpl::eval_if<boost::is_pointer<U>,
williamr@2:             mpl::identity<smart_cast_impl::pointer<T> >,
williamr@2:         // else
williamr@2:         BOOST_DEDUCED_TYPENAME mpl::eval_if<boost::is_reference<U>,
williamr@2:             mpl::identity<smart_cast_impl::reference<T> >,
williamr@2:         // else
williamr@2:             mpl::identity<smart_cast_impl::error<T>
williamr@2:         >
williamr@2:         >
williamr@2:         >
williamr@2:         >::type typex;
williamr@2:     return typex::cast(u);
williamr@2: }
williamr@2: 
williamr@2: // this implements:
williamr@2: // smart_cast_reference<Target &>(Source & s)
williamr@2: template<class T, class U>
williamr@2: T smart_cast_reference(U & u) {
williamr@2:     return smart_cast_impl::reference<T>::cast(u);
williamr@2: }
williamr@2: 
williamr@2: } // namespace boost
williamr@2: 
williamr@2: #endif // BOOST_SMART_CAST_HPP