ChaiScript/include/chaiscript/dispatchkit/dynamic_cast_conversion.hpp

// This file is distributed under the BSD License.
// See "license.txt" for details.
// Copyright 2009-2011, Jonathan Turner (jonathan@emptycrate.com)
// and Jason Turner (jason@emptycrate.com)
// http://www.chaiscript.com

#ifndef CHAISCRIPT_DYNAMIC_CAST_CONVERSION_HPP_
#define CHAISCRIPT_DYNAMIC_CAST_CONVERSION_HPP_

#include "type_info.hpp"
#include "boxed_value.hpp"
#include "boxed_cast_helper.hpp"
#include "bad_boxed_cast.hpp"

namespace chaiscript
{
  namespace exception
  {
    class bad_boxed_dynamic_cast : public bad_boxed_cast
    {
      public:
        bad_boxed_dynamic_cast(const Type_Info &t_from, const std::type_info &t_to,
            const std::string &t_what) throw()
          : bad_boxed_cast(t_from, t_to, t_what)
        {
        }

        bad_boxed_dynamic_cast(const Type_Info &t_from, const std::type_info &t_to) throw()
          : bad_boxed_cast(t_from, t_to)
        {
        }

        bad_boxed_dynamic_cast(const std::string &w) throw()
          : bad_boxed_cast(w)
        {
        }

        virtual ~bad_boxed_dynamic_cast() throw() {}
    };
  }

  namespace detail
  {
    class Dynamic_Conversion
    {
      public:
        virtual Boxed_Value convert(const Boxed_Value &derived) = 0;
        const Type_Info &base()
        {
          return m_base;
        }
        const Type_Info &derived()
        {
          return m_derived;
        }

      protected:
        Dynamic_Conversion(const Type_Info &t_base, const Type_Info &t_derived)
          : m_base(t_base), m_derived(t_derived)
        {
        }

      private:
        Type_Info m_base;
        Type_Info m_derived;

    };

    template<typename Base, typename Derived>
    class Dynamic_Conversion_Impl : public Dynamic_Conversion
    {
      public:
        Dynamic_Conversion_Impl()
          : Dynamic_Conversion(user_type<Base>(), user_type<Derived>())
        {
        }

        virtual Boxed_Value convert(const Boxed_Value &t_derived)
        {
          if (t_derived.get_type_info().bare_equal(user_type<Derived>()))
          {
            if (t_derived.is_pointer())
            {
              // Dynamic cast out the contained boxed value, which we know is the type we want
              if (t_derived.is_const())
              {
                std::shared_ptr<const Base> data 
                  = std::dynamic_pointer_cast<const Base>(detail::Cast_Helper<std::shared_ptr<const Derived> >::cast(t_derived));
                if (!data)
                {
                  throw std::bad_cast();
                }

                return Boxed_Value(data);
              } else {
                std::shared_ptr<Base> data 
                  = std::dynamic_pointer_cast<Base>(detail::Cast_Helper<std::shared_ptr<Derived> >::cast(t_derived));

                if (!data)
                {
                  throw std::bad_cast();
                }

                return Boxed_Value(data);
              }
            } else {
              // Pull the reference out of the contained boxed value, which we know is the type we want
              if (t_derived.is_const())
              {
                const Derived &d = detail::Cast_Helper<const Derived &>::cast(t_derived);
                const Base &data = dynamic_cast<const Base &>(d);
                return Boxed_Value(std::cref(data));
              } else {
                Derived &d = detail::Cast_Helper<Derived &>::cast(t_derived);
                Base &data = dynamic_cast<Base &>(d);
                return Boxed_Value(std::ref(data));
              }
            }
          } else {
            throw exception::bad_boxed_dynamic_cast(t_derived.get_type_info(), typeid(Base), "Unknown dynamic_cast_conversion");
          }
        }
    };


    class Dynamic_Conversions
    {
      public:
        static inline Dynamic_Conversions &get()
        {
          static Dynamic_Conversions obj;
          return obj;
        }

        template<typename Base, typename Derived>
        static std::shared_ptr<Dynamic_Conversion> create()
        {
          std::shared_ptr<Dynamic_Conversion> conversion(new Dynamic_Conversion_Impl<Base, Derived>());

          /// \todo this is a hack and a kludge. The idea is to make sure that
          ///       the conversion is registered both in the module's notion of the static conversion object
          ///       and in the global notion of the static conversion object
          ///       someday this will almost certainly have to change. Maybe it is time for ChaiScript
          ///       to become a library?
          Dynamic_Conversions::get().add_conversion(conversion);
          return conversion;
        }

        template<typename InItr>
        void cleanup(InItr begin, const InItr &end)
        {
          chaiscript::detail::threading::unique_lock<chaiscript::detail::threading::shared_mutex> l(m_mutex);

          while (begin != end)
          {
            if (begin->unique())
            {
              m_conversions.erase(begin->get());
            }

            ++begin;
          }
        }

        void add_conversion(const std::shared_ptr<Dynamic_Conversion> &conversion)
        {
          chaiscript::detail::threading::unique_lock<chaiscript::detail::threading::shared_mutex> l(m_mutex);

          m_conversions.insert(conversion.get());
        }

        bool has_conversion(const Type_Info &base, const Type_Info &derived) const
        {
          chaiscript::detail::threading::shared_lock<chaiscript::detail::threading::shared_mutex> l(m_mutex);

          return find(base, derived) != m_conversions.end();
        }


        Dynamic_Conversion *get_conversion(const Type_Info &base, const Type_Info &derived) const
        {
          chaiscript::detail::threading::shared_lock<chaiscript::detail::threading::shared_mutex> l(m_mutex);

          std::set<Dynamic_Conversion *>::const_iterator itr =
            find(base, derived);

          if (itr != m_conversions.end())
          {
            return *itr;
          } else {
            throw std::out_of_range("No such conversion exists from " + derived.bare_name() + " to " + base.bare_name());
          }
        }

      private:
        Dynamic_Conversions() {}

        std::set<Dynamic_Conversion *>::const_iterator find(
            const Type_Info &base, const Type_Info &derived) const
        {
          for (std::set<Dynamic_Conversion *>::const_iterator itr = m_conversions.begin();
               itr != m_conversions.end();
               ++itr)
          {
            if ((*itr)->base().bare_equal(base) && (*itr)->derived().bare_equal(derived))
            {
              return itr;
            }
          }

          return m_conversions.end();
        }

        mutable chaiscript::detail::threading::shared_mutex m_mutex;
        std::set<Dynamic_Conversion *> m_conversions;
    };
  }

  typedef std::shared_ptr<chaiscript::detail::Dynamic_Conversion> Dynamic_Cast_Conversion;

  /// \brief Used to register a base / parent class relationship with ChaiScript. Necessary if you
  ///        want automatic conversions up your inheritance hierarchy.
  ///
  /// Create a new base class registration for applying to a module or to the chaiscript engine
  /// Currently, due to limitations in module loading on Windows, and for the sake of portability,
  /// if you have a type that is introduced in a loadable module and is used by multiple modules
  /// (through a tertiary dll that is shared between the modules, static linking the new type
  /// into both loadable modules would not be portable), you need to register the base type
  /// relationship in all modules that use the newly added type in a polymorphic way.
  ///
  /// Example:
  /// \code
  /// class Base
  /// {};
  /// class Derived : public Base
  /// {};
  ///
  /// chaiscript::ChaiScript chai;
  /// chai.add(chaiscript::base_class<Base, Derived>());
  /// \endcode
  /// 
  /// \todo Move share static type registration code into a mechanism that allows it to be properly
  ///       shared by all modules
  template<typename Base, typename Derived>
  Dynamic_Cast_Conversion base_class()
  {
    //Can only be used with related polymorphic types
    //may be expanded some day to support conversions other than child -> parent
    BOOST_STATIC_ASSERT((std::is_base_of<Base,Derived>::value));
    BOOST_STATIC_ASSERT(std::is_polymorphic<Base>::value);
    BOOST_STATIC_ASSERT(std::is_polymorphic<Derived>::value);

    return detail::Dynamic_Conversions::create<Base, Derived>();
  }

  namespace detail
  {
    template<typename Base, typename Derived>
      bool dynamic_cast_converts()
      {
        return dynamic_cast_converts(user_type<Base>(), user_type<Derived>());
      }

    static bool dynamic_cast_converts(const Type_Info &base, const Type_Info &derived)
    {
      return detail::Dynamic_Conversions::get().has_conversion(base, derived);
    }

    template<typename Base>
      Boxed_Value boxed_dynamic_cast(const Boxed_Value &derived)
      {
        try {
          return detail::Dynamic_Conversions::get().get_conversion(user_type<Base>(), derived.get_type_info())->convert(derived);
        } catch (const std::out_of_range &) {
          throw exception::bad_boxed_dynamic_cast(derived.get_type_info(), typeid(Base), "No known conversion");
        } catch (const std::bad_cast &) {
          throw exception::bad_boxed_dynamic_cast(derived.get_type_info(), typeid(Base), "Unable to perform dynamic_cast operation");
        }
      }
  }
}


#endif