+ ((char *)(obj) - offsetof(struct cls##__ilayout, chead)))
+
+/* --- @SOD__CAR@ --- *
+ *
+ * Arguments: @...@ = a nonempty list of arguments
+ *
+ * Returns: The first argument only.
+ */
+
+#if __STDC_VERSION__ >= 199901
+# define SOD__CAR(...) SOD__CARx(__VA_LIST__, _)
+# define SOD__CARx(a, ...) a
+#endif
+
+/*----- Utility macros ----------------------------------------------------*/
+
+/* --- @SOD_CLASSOF@ --- *
+ *
+ * Arguments: @p@ = pointer to an instance chain
+ *
+ * Returns: A pointer to the instance's class, as a const SodClass.
+ */
+
+#define SOD_CLASSOF(obj) ((const SodClass *)(obj)->_vt->_class)