[glib: 1/2] gtype: Document type for iface_default_init() function

[Simon McVittie <smcv src gnome org>]

commit 154b24c055a3de38f6a33a3ec297e416150c4f0e
Author: Philip Withnall <withnall endlessm com>
Date:   Thu Dec 27 23:46:42 2018 +0000

    gtype: Document type for iface_default_init() function
    
    And mention why it’s not a GInterfaceInitFunc as people who have read
    the GObject docs cover-to-cover might expect.
    
    Signed-off-by: Philip Withnall <withnall endlessm com>

 gobject/gtype.h | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/gobject/gtype.h b/gobject/gtype.h
index 0d366e67b..70181cd5c 100644
--- a/gobject/gtype.h
+++ b/gobject/gtype.h
@@ -1753,6 +1753,12 @@ guint     g_type_get_type_registration_serial (void);
  * name `t_n ## _default_init`, and the interface structure to have the
  * name `TN ## Interface`.
  *
+ * The initialization function has signature
+ * `static void t_n ## _default_init (TypeName##Interface *klass);`, rather than
+ * the full #GInterfaceInitFunc signature, for brevity and convenience. If you
+ * need to use an initialization function with an `iface_data` argument, you
+ * must write the #GTypeInterface definitions manually.
+ *
  * Since: 2.24
  */
 #define G_DEFINE_INTERFACE(TN, t_n, T_P)                   G_DEFINE_INTERFACE_WITH_CODE(TN, t_n, T_P, ;)