diff --git a/core/include/blue/core/macros.h b/core/include/blue/core/macros.h
index 47a82bc..15816db 100644
--- a/core/include/blue/core/macros.h
+++ b/core/include/blue/core/macros.h
@@ -7,10 +7,8 @@
 #include <blue/core/type.h>
 #include <stdlib.h>
 
-#define __B_IFACE_I0(p, x)  p##x
-#define __B_IFACE_I1(p, x)  __B_IFACE_I0(p, x)
-
-#define B_TYPE_FWDREF(name) struct _b_object
+#define __B_IFACE_I0(p, x) p##x
+#define __B_IFACE_I1(p, x) __B_IFACE_I0(p, x)
 
 /* Type definitions macros (for use in .c source file) */
 
@@ -65,6 +63,7 @@
 		&type_info->t_interfaces[type_info->t_nr_interfaces++])
 #define B_TYPE_CLASS(class_struct)                                             \
 	type_info->t_class_size = sizeof(class_struct)
+#define B_TYPE_FLAGS(flags)        type_info->t_flags = (flags)
 #define B_TYPE_INSTANCE_INIT(func) type_info->t_instance_init = (func)
 #define B_TYPE_INSTANCE_FINI(func) type_info->t_instance_fini = (func)
 
@@ -114,23 +113,46 @@
 
 /* Other macros */
 
-#define B_CLASS_DISPATCH_VIRTUAL(type_name, type_id, object, func, ...)        \
+#define B_CLASS_DISPATCH_VIRTUAL(                                              \
+	type_name, type_id, default_value, func, object, ...)                  \
 	do {                                                                   \
 		type_name##_class *iface                                       \
 			= b_object_get_interface(object, type_id);             \
 		if (iface && iface->func) {                                    \
-			return iface->func(__VA_ARGS__);                       \
+			return iface->func(object, __VA_ARGS__);               \
+		} else {                                                       \
+			return default_value;                                  \
 		}                                                              \
 	} while (0)
-#define B_CLASS_DISPATCH_VIRTUAL_V(type_name, type_id, object, func, ...)      \
+#define B_CLASS_DISPATCH_VIRTUAL_0(type_name, type_id, default_value, func, object) \
+	do {                                                                        \
+		type_name##_class *iface                                            \
+			= b_object_get_interface(object, type_id);                  \
+		if (iface && iface->func) {                                         \
+			return iface->func(object);                                 \
+		} else {                                                            \
+			return default_value;                                       \
+		}                                                                   \
+	} while (0)
+#define B_CLASS_DISPATCH_VIRTUAL_V(type_name, type_id, func, object, ...)      \
 	do {                                                                   \
 		type_name##_class *iface                                       \
 			= b_object_get_interface(object, type_id);             \
 		if (iface && iface->func) {                                    \
-			iface->func(__VA_ARGS__);                              \
+			iface->func(object, __VA_ARGS__);                      \
 			return;                                                \
 		}                                                              \
 	} while (0)
+#define B_CLASS_DISPATCH_VIRTUAL_V0(type_name, type_id, func, object)          \
+	do {                                                                   \
+		type_name##_class *iface                                       \
+			= b_object_get_interface(object, type_id);             \
+		if (iface && iface->func) {                                    \
+			iface->func(object);                                   \
+			return;                                                \
+		}                                                              \
+	} while (0)
+
 #define B_CLASS_DISPATCH_STATIC(type_id, func_name, obj, ...)                  \
 	do {                                                                   \
 		void *priv = b_object_get_private(obj, type_id);               \