First cast up chain, if that fails, cast down

include/chaiscript/dispatchkit/boxed_cast.hpp

@@ -84,11 +84,18 @@ namespace chaiscript
       if (boost::is_polymorphic<typename detail::Stripped_Type<Type>::type>::value && t_conversions)
       {
         try {
+          std::cout << "trying an up conversion " << typeid(Type).name() << std::endl;
           // We will not catch any bad_boxed_dynamic_cast that is thrown, let the user get it
           // either way, we are not responsible if it doesn't work
           return detail::Cast_Helper<Type>::cast(t_conversions->boxed_dynamic_cast<Type>(bv), t_conversions);
-        } catch (const boost::bad_any_cast &) {
+        } catch (...) {
-          throw exception::bad_boxed_cast(bv.get_type_info(), typeid(Type));
+          try {
+            std::cout << "trying a down conversion " << typeid(Type).name() << std::endl;
+            // try going the other way - down the inheritance graph
+            return detail::Cast_Helper<Type>::cast(t_conversions->boxed_dynamic_down_cast<Type>(bv), t_conversions);
+          } catch (const boost::bad_any_cast &) {
+            throw exception::bad_boxed_cast(bv.get_type_info(), typeid(Type));
+          }
         }
       } else {
         // If it's not polymorphic, just throw the error, don't waste the time on the 

include/chaiscript/dispatchkit/dynamic_cast_conversion.hpp

@@ -48,6 +48,7 @@ namespace chaiscript
     {
       public:
         virtual Boxed_Value convert(const Boxed_Value &derived) const = 0;
+        virtual Boxed_Value convert_down(const Boxed_Value &base) const = 0;
 
         const Type_Info &base()
         {
@@ -72,6 +73,57 @@ namespace chaiscript
 
     };
 
+    template<typename From, typename To> 
+      class Dynamic_Caster
+      {
+        public: 
+          static Boxed_Value cast(const Boxed_Value &t_from)
+          {
+            if (t_from.get_type_info().bare_equal(user_type<From>()))
+            {
+              if (t_from.is_pointer())
+              {
+                // Dynamic cast out the contained boxed value, which we know is the type we want
+                if (t_from.is_const())
+                {
+                  boost::shared_ptr<const To> data 
+                    = boost::dynamic_pointer_cast<const To>(detail::Cast_Helper<boost::shared_ptr<const From> >::cast(t_from, 0));
+                  if (!data)
+                  {
+                    throw std::bad_cast();
+                  }
+
+                  return Boxed_Value(data);
+                } else {
+                  boost::shared_ptr<To> data 
+                    = boost::dynamic_pointer_cast<To>(detail::Cast_Helper<boost::shared_ptr<From> >::cast(t_from, 0));
+
+                  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_from.is_const())
+                {
+                  const From &d = detail::Cast_Helper<const From &>::cast(t_from, 0);
+                  const To &data = dynamic_cast<const To &>(d);
+                  return Boxed_Value(boost::cref(data));
+                } else {
+                  From &d = detail::Cast_Helper<From &>::cast(t_from, 0);
+                  To &data = dynamic_cast<To &>(d);
+                  return Boxed_Value(boost::ref(data));
+                }
+              }
+            } else {
+              throw exception::bad_boxed_dynamic_cast(t_from.get_type_info(), typeid(To), "Unknown dynamic_cast_conversion");
+            }
+          }
+      };
+
     template<typename Base, typename Derived>
       class Dynamic_Conversion_Impl : public Dynamic_Conversion
     {
@@ -81,50 +133,14 @@ namespace chaiscript
         {
         }
 
+        virtual Boxed_Value convert_down(const Boxed_Value &t_base) const
+        {
+          return Dynamic_Caster<Base, Derived>::cast(t_base);
+        }
+
         virtual Boxed_Value convert(const Boxed_Value &t_derived) const
         {
-          if (t_derived.get_type_info().bare_equal(user_type<Derived>()))
+          return Dynamic_Caster<Derived, Base>::cast(t_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())
-              {
-                boost::shared_ptr<const Base> data 
-                  = boost::dynamic_pointer_cast<const Base>(detail::Cast_Helper<boost::shared_ptr<const Derived> >::cast(t_derived, 0));
-                if (!data)
-                {
-                  throw std::bad_cast();
-                }
-
-                return Boxed_Value(data);
-              } else {
-                boost::shared_ptr<Base> data 
-                  = boost::dynamic_pointer_cast<Base>(detail::Cast_Helper<boost::shared_ptr<Derived> >::cast(t_derived, 0));
-
-                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, 0);
-                const Base &data = dynamic_cast<const Base &>(d);
-                return Boxed_Value(boost::cref(data));
-              } else {
-                Derived &d = detail::Cast_Helper<Derived &>::cast(t_derived, 0);
-                Base &data = dynamic_cast<Base &>(d);
-                return Boxed_Value(boost::ref(data));
-              }
-            }
-          } else {
-            throw exception::bad_boxed_dynamic_cast(t_derived.get_type_info(), typeid(Base), "Unknown dynamic_cast_conversion");
-          }
         }
     };
   }
@@ -155,7 +171,7 @@ namespace chaiscript
 
       bool dynamic_cast_converts(const Type_Info &base, const Type_Info &derived) const
       {
-        return has_conversion(base, derived);
+        return has_conversion(base, derived) || has_conversion(derived, base);
       }
 
       template<typename Base>
@@ -170,6 +186,19 @@ namespace chaiscript
           }
         }
 
+      template<typename Derived>
+        Boxed_Value boxed_dynamic_down_cast(const Boxed_Value &base) const
+        {
+          try {
+            return get_conversion(base.get_type_info(), user_type<Derived>())->convert_down(base);
+          } catch (const std::out_of_range &) {
+            throw exception::bad_boxed_dynamic_cast(base.get_type_info(), typeid(Derived), "No known conversion");
+          } catch (const std::bad_cast &) {
+            throw exception::bad_boxed_dynamic_cast(base.get_type_info(), typeid(Derived), "Unable to perform dynamic_cast operation");
+          }
+        }
+
+
       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);

unittests/inheritance.chai

@@ -19,8 +19,9 @@ assert_equal(23, t.val)
 // in a shared_ptr<TestBaseType>. This is testing our ability
 // to detect that and do the down casting for the user automatically
 // at runtime
-var d := derived_type_factory();
 
 assert_equal(t.derived_only_func(), 19);
+
+var d := derived_type_factory();
 assert_equal(d.derived_only_func(), 19);