+typedef struct _GCredentials GCredentials;
+typedef struct _GUnixCredentialsMessage GUnixCredentialsMessage;
+typedef struct _GUnixFDList GUnixFDList;
+typedef struct _GDBusMessage GDBusMessage;
+typedef struct _GDBusConnection GDBusConnection;
+typedef struct _GDBusProxy GDBusProxy;
+typedef struct _GDBusMethodInvocation GDBusMethodInvocation;
+typedef struct _GDBusServer GDBusServer;
+typedef struct _GDBusAuthObserver GDBusAuthObserver;
+typedef struct _GDBusErrorEntry GDBusErrorEntry;
+typedef struct _GDBusInterfaceVTable GDBusInterfaceVTable;
+typedef struct _GDBusSubtreeVTable GDBusSubtreeVTable;
+typedef struct _GDBusAnnotationInfo GDBusAnnotationInfo;
+typedef struct _GDBusArgInfo GDBusArgInfo;
+typedef struct _GDBusMethodInfo GDBusMethodInfo;
+typedef struct _GDBusSignalInfo GDBusSignalInfo;
+typedef struct _GDBusPropertyInfo GDBusPropertyInfo;
+typedef struct _GDBusInterfaceInfo GDBusInterfaceInfo;
+typedef struct _GDBusNodeInfo GDBusNodeInfo;
+
+/**
+ * GCancellableSourceFunc:
+ * @cancellable: the #GCancellable
+ * @user_data: data passed in by the user.
+ *
+ * This is the function type of the callback used for the #GSource
+ * returned by g_cancellable_source_new().
+ *
+ * Returns: it should return %FALSE if the source should be removed.
+ *
+ * Since: 2.28
+ */
+typedef gboolean (*GCancellableSourceFunc) (GCancellable *cancellable,
+ gpointer user_data);
+
+/**
+ * GPollableSourceFunc:
+ * @pollable_stream: the #GPollableInputStream or #GPollableOutputStream
+ * @user_data: data passed in by the user.
+ *
+ * This is the function type of the callback used for the #GSource
+ * returned by g_pollable_input_stream_create_source() and
+ * g_pollable_output_stream_create_source().
+ *
+ * Returns: it should return %FALSE if the source should be removed.
+ *
+ * Since: 2.28
+ */
+typedef gboolean (*GPollableSourceFunc) (GObject *pollable_stream,
+ gpointer user_data);
+
+typedef struct _GDBusInterface GDBusInterface; /* Dummy typedef */
+typedef struct _GDBusInterfaceSkeleton GDBusInterfaceSkeleton;
+typedef struct _GDBusObject GDBusObject; /* Dummy typedef */
+typedef struct _GDBusObjectSkeleton GDBusObjectSkeleton;
+typedef struct _GDBusObjectProxy GDBusObjectProxy;
+typedef struct _GDBusObjectManager GDBusObjectManager; /* Dummy typedef */
+typedef struct _GDBusObjectManagerClient GDBusObjectManagerClient;
+typedef struct _GDBusObjectManagerServer GDBusObjectManagerServer;
+
+/**
+ * GDBusProxyTypeFunc:
+ * @manager: A #GDBusObjectManagerClient.
+ * @object_path: The object path of the remote object.
+ * @interface_name: (allow-none): The interface name of the remote object or %NULL if a #GDBusObjectProxy #GType is requested.
+ * @user_data: User data.
+ *
+ * Function signature for a function used to determine the #GType to
+ * use for an interface proxy (if @interface_name is not %NULL) or
+ * object proxy (if @interface_name is %NULL).
+ *
+ * This function is called in the
+ * <link linkend="g-main-context-push-thread-default">thread-default main loop</link>
+ * that @manager was constructed in.
+ *
+ * Returns: A #GType to use for the remote object. The returned type
+ * must be a #GDBusProxy<!-- -->- or #GDBusObjectProxy<!-- -->-derived
+ * type.
+ *
+ * Since: 2.30
+ */
+typedef GType (*GDBusProxyTypeFunc) (GDBusObjectManagerClient *manager,
+ const gchar *object_path,
+ const gchar *interface_name,
+ gpointer user_data);