[glib] docs: Add an example of G_DEFINE_BOXED_TYPE

[Emmanuele Bassi <ebassi src gnome org>]

commit 5e7e058a9c26fa735386cf45b41ad91cc7768137
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Mon Apr 20 14:11:12 2015 +0100

    docs: Add an example of G_DEFINE_BOXED_TYPE
    
    Mention that the GType of the boxed type is stored inside the
    g_define_type_id variable.
    
    See bug: https://bugzilla.gnome.org/show_bug.cgi?id=723394

 gobject/gtype.h |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)
---
diff --git a/gobject/gtype.h b/gobject/gtype.h
index 68bc051..611e637 100644
--- a/gobject/gtype.h
+++ b/gobject/gtype.h
@@ -2021,7 +2021,17 @@ type_name##_get_type (void) \
  * A convenience macro for boxed type implementations.
  * Similar to G_DEFINE_BOXED_TYPE(), but allows to insert custom code into the
  * type_name_get_type() function, e.g. to register value transformations with
- * g_value_register_transform_func().
+ * g_value_register_transform_func(), for instance:
+ *
+ * |[<!-- language="C" -->
+ * G_DEFINE_BOXED_TYPE_WITH_CODE (GdkRectangle, gdk_rectangle,
+ *                                gdk_rectangle_copy,
+ *                                gdk_rectangle_free,
+ *                                register_rectangle_transform_funcs (g_define_type_id))
+ * ]|
+ *
+ * Similarly to the %G_DEFINE_TYPE family of macros, the #GType of the newly
+ * defined boxed type is exposed in the `g_define_type_id` variable.
  *
  * Since: 2.26
  */