Macro impl_from_user_facing_event_for_interface_event_enum 

macro_rules! impl_from_user_facing_event_for_interface_event_enum {
    ($inner_type:ty, $outer_type:ty, $inner_variant:path) => { ... };
}

Expands to a conversion given the user facing event type and outer Event::Interface(<InterfaceEnum>) variant., the enum type and outtermost variant.

impl_from_user_facing_event_for_interface_event_enum!(StateChangedEvent, ObjectEvents, ObjectEvents::StateChanged);

expands to:

impl From<StateChangedEvent> for ObjectEvents {
    fn from(specific_event: StateChangedEvent) -> ObjectEvents {
        ObjectEvents::StateChanged(specific_event)
    }
}