[Newbie] When to use *_IS_* macro?

[Guilhem Bonnefille <guilhem bonnefille gmail com>]

Hi,

In order to keep a code as clean as possible, I'm currently thinking about removing/adding code.

The current object of my thoughts is *_IS_* macros, using G_TYPE_CHECK_INSTANCE_TYPE. In which circumstance should we use this macro (and related) and when not use them?

My understanding is these macro allow safe "down-casting". So I need to use them when a cast is necessary, but avoid them in other case.

For exemple, in Gtk tutorial[1] I can read the following functions:

static void

gtk_dial_destroy (GtkObject *object)

{

  GtkDial *dial;

  g_return_if_fail (object != NULL);

  g_return_if_fail (GTK_IS_DIAL (object));

  dial = GTK_DIAL (object);

  if (dial->adjustment)

    gtk_object_unref (GTK_OBJECT (dial->adjustment));

  if (GTK_OBJECT_CLASS (parent_class)->destroy)

    (* GTK_OBJECT_CLASS (parent_class)->destroy) (object);

}

GtkAdjustment*

gtk_dial_get_adjustment (GtkDial *dial)

{

  g_return_val_if_fail (dial != NULL, NULL);

  g_return_val_if_fail (GTK_IS_DIAL (dial), NULL);

  return dial->adjustment;

}

In my mind, GTK_IS_DIAL and GTK_DIAL are necessary in gtk_dial_destroy as the argument is not GtkDial but GtkObject.

In the other hand, GTK_IS_DIAL seems not necessary in gtk_dial_get_adjustment as C compiler will ensure (gruik cast excepted) that argument is in the right type.

Can I consider to remove *_IS_* in codes like gtk_dial_get_adjustment or is it a best practice to always call such macro?

[1] http://developer.gnome.org/gtk-tutorial/stable/x2310.html

--
Guilhem BONNEFILLE
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