+/**
+ * This callback function returns the hashcode of a key.
+ *
+ * \param this is a pointer to the itemkeyfun record from where this
+ * callback got invoked
+ *
+ * \param key is the key to produce a hascode for
+ *
+ * \returns the hashcode which is a vector_index (i.e. unsigned long)
+ *
+ * The hashcode is used for indexing into the backing vector for
+ * finding the an item via its key. The same key must map consistently
+ * to the same hashcode while the hashtable contains an item with that
+ * key. Different keys map map to the same hashcode, in which case the
+ * vector placement is made at the first empty or hole slot following
+ * the hashcode index.
+ */
+static unsigned long tupleitem_hashcode(void *this,void *key) {