# Class Uq_engines.engine_mixin

    class ['a] engine_mixin : 'a engine_state -> Unixqueue.event_system -> object .. end

A useful class fragment that implements `state` and `request_notification`.

    method state : 'a engine_state

    method private set_state : 'a engine_state -> unit

    method request_notification : (unit -> bool) -> unit

    method private notify : unit -> unit

    method event_system : Unixqueue.event_system