- tags->iterator = message->doc.termlist_begin ();
- tags->iterator.skip_to (_find_prefix ("tag"));
- tags->iterator_end = message->doc.termlist_end ();
+/* The assertion is to ensure that 'type' is a derivative of
+ * notmuch_terms_t in that it contains a notmuch_terms_t as its first
+ * member. We do this by name of 'terms' as opposed to type, because
+ * that's as clever as I've been so far. */
+#define _notmuch_terms_create_type(ctx, doc, prefix_name, type) \
+ (COMPILE_TIME_ASSERT(offsetof(type, terms) == 0), \
+ (type *) _notmuch_terms_create (ctx, doc, prefix_name))