diff --git a/core/class.c b/core/class.c
index 4871c80..c21f954 100644
--- a/core/class.c
+++ b/core/class.c
@@ -6,7 +6,7 @@
 #include <stdlib.h>
 #include <string.h>
 
-void *z__b_class_get_interface(struct _b_class *c, const union b_type *id)
+void *b_class_get_interface(const struct _b_class *c, const union b_type *id)
 {
 	const struct b_type_registration *type_reg = c->c_type;
 	struct b_type_component *comp
diff --git a/core/include/blue/core/class.h b/core/include/blue/core/class.h
index e09776b..6c9cbd6 100644
--- a/core/include/blue/core/class.h
+++ b/core/include/blue/core/class.h
@@ -8,10 +8,6 @@
 
 typedef struct _b_class b_class;
 
-#define b_class_get_interface(class, interface_struct, interface_id)           \
-	((interface_struct *)z__b_class_get_interface(                         \
-		B_CLASS(class), interface_id));
-
-BLUE_API void *z__b_class_get_interface(b_class *c, b_type id);
+BLUE_API void *b_class_get_interface(const b_class *c, b_type id);
 
 #endif
diff --git a/core/include/blue/core/macros.h b/core/include/blue/core/macros.h
index 7932822..47a82bc 100644
--- a/core/include/blue/core/macros.h
+++ b/core/include/blue/core/macros.h
@@ -19,10 +19,10 @@
 	{
 #define B_TYPE_CLASS_DEFINITION_END(type_name) }
 
-#define B_TYPE_CLASS_INTERFACE_BEGIN(interface_name, interface_id)                \
-	interface_name##_class *__B_IFACE_I1(iface, __LINE__)                     \
-		= b_class_get_interface(p, interface_name##_class, interface_id); \
-	if (__B_IFACE_I1(iface, __LINE__)) {                                      \
+#define B_TYPE_CLASS_INTERFACE_BEGIN(interface_name, interface_id)             \
+	interface_name##_class *__B_IFACE_I1(iface, __LINE__)                  \
+		= b_class_get_interface(p, interface_id);                      \
+	if (__B_IFACE_I1(iface, __LINE__)) {                                   \
 		interface_name##_class *iface = __B_IFACE_I1(iface, __LINE__);
 #define B_TYPE_CLASS_INTERFACE_END(interface_name, interface_id) }
 #define B_INTERFACE_ENTRY(slot)                                  iface->slot
diff --git a/core/include/blue/core/object.h b/core/include/blue/core/object.h
index c8d62d7..f4accba 100644
--- a/core/include/blue/core/object.h
+++ b/core/include/blue/core/object.h
@@ -15,19 +15,20 @@ struct b_stream;
 typedef struct _b_object b_object;
 
 typedef struct _b_object_class {
-	void (*to_string)(b_object *, struct b_stream *);
+	void (*to_string)(const b_object *, struct b_stream *);
 } b_object_class;
 
 BLUE_API b_type b_object_get_type(void);
 
-BLUE_API void *b_object_get_private(b_object *object, b_type type);
-BLUE_API void *b_object_get_protected(b_object *object, b_type type);
-BLUE_API void *b_object_get_interface(b_object *object, b_type type);
+BLUE_API void *b_object_get_private(const b_object *object, b_type type);
+BLUE_API void *b_object_get_protected(const b_object *object, b_type type);
+BLUE_API void *b_object_get_interface(const b_object *object, b_type type);
 
 BLUE_API b_object *b_object_ref(b_object *p);
 BLUE_API void b_object_unref(b_object *p);
 
 BLUE_API b_object *b_object_create(b_type type);
-BLUE_API void b_object_to_string(b_object *p, struct b_stream *out);
+BLUE_API void b_object_to_string(const b_object *p, struct b_stream *out);
+BLUE_API bool b_object_is_type(const b_object *p, b_type type);
 
 #endif
diff --git a/core/object.c b/core/object.c
index 6ebb610..72b82fa 100644
--- a/core/object.c
+++ b/core/object.c
@@ -77,7 +77,7 @@ void b_object_to_string(struct _b_object *p, struct b_stream *out)
 	b_stream_write_fmt(out, NULL, "<%s@%p>", p->obj_type->r_info->t_name, p);
 }
 
-void *b_object_get_private(struct _b_object *object, b_type type)
+void *b_object_get_private(const struct _b_object *object, b_type type)
 {
 	if (b_type_id_compare(&object->obj_type->r_info->t_id, type) == 0) {
 		return (char *)object + object->obj_main_priv_offset;
@@ -92,7 +92,7 @@ void *b_object_get_private(struct _b_object *object, b_type type)
 	return (char *)object + comp->c_instance_private_data_offset;
 }
 
-void *b_object_get_protected(struct _b_object *object, b_type type)
+void *b_object_get_protected(const struct _b_object *object, b_type type)
 {
 	struct b_type_component *comp
 		= b_type_get_component(&object->obj_type->r_components, type);
@@ -103,9 +103,9 @@ void *b_object_get_protected(struct _b_object *object, b_type type)
 	return (char *)object + comp->c_instance_protected_data_offset;
 }
 
-void *b_object_get_interface(struct _b_object *object, b_type type)
+void *b_object_get_interface(const struct _b_object *object, b_type type)
 {
-	return z__b_class_get_interface(object->obj_type->r_class, type);
+	return b_class_get_interface(object->obj_type->r_class, type);
 }
 
 struct _b_object *b_object_ref(struct _b_object *p)