+#define GET_OBJ(obj, type, o, desc) \
+ type **(o) = NULL; \
+\
+ Data_Get_Struct ((obj), type *, (o)); \
+\
+ if (!*(o)) { \
+ rb_raise (rb_eException, desc " destroyed already"); \
+ return Qnil; \
+ }
+
+#define CHECK_BOOL(val) \
+ if (TYPE ((val)) != T_TRUE && TYPE ((val)) != T_FALSE) { \
+ rb_raise (rb_eTypeError, \
+ "wrong argument type %s (expected true or false)", \
+ rb_obj_classname ((val))); \
+ return Qnil; \
+ }
+