gistfile1.scala

// These are my two event classes...
case class Event1(id: Int, eventStartTime: DateTime, entityRoles: EntityRoles)
object Event1 {
  override def toString = "ev1"
  implicit val isTimeStamped: Timestamped[Event1] =
    Timestamped.from(_.eventStartTime)
  implicit val isEntityRoleAware: EntityRoleAware[Event1] =
    EntityRoleAware.from(_.entityRoles.roles)
  implicit val hasOrdering: Ordering[Event1] =
    Ordering.by(e => (e.eventStartTime, e.entityRoles))
}

case class Event2(id: Int, eventStartTime: DateTime, entityRoles: EntityRoles)

object Event2 {
  override def toString = "ev2"
  implicit val isTimeStamped: Timestamped[Event2] =
    Timestamped.from(_.eventStartTime)
  implicit val isEntityRoleAware: EntityRoleAware[Event2] =
    EntityRoleAware.from(_.entityRoles.roles)
  implicit val hasOrdering: Ordering[Event2] =
    Ordering.by(e => (e.eventStartTime, e.entityRoles))
    
    object entityRoles extends Poly1 {
    implicit def event1Case = at[Event1](e => e.entityRoles)

    implicit def event2Case = at[Event2](e => e.entityRoles)
  }
  
}
// These are my events...
type EventCoproduct = Event1 :+: Event2 :+: CNil
val events: List[EventCoproduct] = Random.shuffle(testEvents1 :+: testEvents2 :+: nil)

// When I do this:

ThermometerSource(events)
      .selectPattern[Event1, Event2]((x: EventCoproduct) => (x map entityRoles).select[EntityRoles].get,true)
      
// I get a type error
[error]  found   : au.com.cba.omnia.eventually.core.EntityRoles
[error]  required: K