# A Message received by a Mailbox
# In fact, this is the reification of a call
# Each Message class represent a call to make on `instance` via `invoke`
abstract class Message

	# Type of the class on which `self` make the call
	type E: Object

	# Redef this method so it calls the right one on `instance` (double dispatch)
	fun invoke(instance: E) is abstract
end