Class ConstantExpression

The value that self evaluates to is set via g_object_set() on target. This is repeated whenever self changes to ensure that the object's property stays synchronized with self.

If self's evaluation fails, target's property is not updated. You can ensure that this doesn't happen by using a fallback expression.

Note that this function takes ownership of self. If you want to keep it around, you should [methodGtk.Expression.ref] it beforehand.

The GType of value will be the type given by [methodGtk.Expression.get_value_type].

It is possible that expressions cannot be evaluated - for example when the expression references objects that have been destroyed or set to NULL. In that case value will remain empty and FALSE will be returned.

This type is constant and will not change over the lifetime of this expression.

A static expression will never change its result when [methodGtk.Expression.evaluate] is called on it with the same arguments.

That means a call to [methodGtk.Expression.watch] is not necessary because it will never trigger a notify.

If the reference was the last, the resources associated to the self are freed.

The notify function will be called whenever the evaluation of self may have changed.

GTK cannot guarantee that the evaluation did indeed change when the notify gets invoked, but it guarantees the opposite: When it did in fact change, the notify will be invoked.