-/** \brief Malloc and set the data associated with the current process. */
-#define gras_userdata_new(type) (gras_userdata_set(xbt_new0(type,1)),gras_userdata_get())
+/** \brief Malloc and set the data associated with the current process.
+ *
+ * @warnig gras_userdata_new() expects the pointed type, not the
+ * pointer type. We know it'a a bit troublesome, but it seems like
+ * the only solution since this macro has to compute the size to
+ * malloc and should thus know the pointed type.
+ *
+ * You'll find an example in the tutorial: \ref GRAS_tut_tour_globals
+ */
+#define gras_userdata_new(type) ((type*)gras_userdata_set(xbt_new0(type,1)))