[Vala] Virtual methods in interfaces

[James Moschou <james moschou gmail com>]

Is is possible to mark methods as virtual in interfaces, as a
mechanism of providing default implementations?

If I do

interface Interface {
 public virtual void function () {
   // Default
 }
}

class Class : Object, Interface {
 public override void function () {
   // Custom
 }
}

The compiler says that no method to override was found.

Regards
James