X-Git-Url: https://git.distorted.org.uk/~mdw/sod/blobdiff_plain/267dd3e78997ba6f5a0801c0afab2148dd049f16..64d1ecf751f542782b5ffb9c9469c70d92f423de:/lib/sod.h

diff --git a/lib/sod.h b/lib/sod.h
index 919b927..efac06b 100644
--- a/lib/sod.h
+++ b/lib/sod.h
@@ -53,7 +53,7 @@ struct sod_vtable {
  * these.
  */
 struct sod_instance {
-  struct sod_vtable *_vt;		/* Pointer to (chain's) vtable */
+  const struct sod_vtable *_vt;		/* Pointer to (chain's) vtable */
 };
 
 /* Information about a particular chain of superclasses.  In each class,
@@ -76,14 +76,15 @@ struct sod_chain {
  * Arguments:	@chead@ = nickname of target chain's head
  *		@obj@ = pointer to an instance chain
  *
- * Returns:	Pointer to target chain, as a @char *@.
+ * Returns:	Pointer to target chain, as a @void *@.
  *
  * Use:		Utility for implementing cross-chain upcasts.  It's probably
  *		not that clever to use this macro directly; it's used to make
  *		the automatically-generated upcast macros more palatable.
  */
 
-#define SOD_XCHAIN(chead, obj) ((char *)(obj) + (obj)->_vt->_off_##chead)
+#define SOD_XCHAIN(chead, obj)						\
+  ((void *)((char *)(obj) + (obj)->_vt->_off_##chead))
 
 /* --- @SOD_OFFSETDIFF@ --- *
  *
@@ -124,6 +125,18 @@ struct sod_chain {
   ((struct cls##__ilayout *)						\
    ((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@ --- *