Created
September 27, 2017 04:45
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Scala Workflow using forSome existentials Raw (with proper scope this time)
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import scala.language.existentials | |
// Simple laboratory exercise that uses existentials everywhere for the Transition. | |
// But these existentials are not bound to much restriction and are not recognized | |
// to be compatible with the built list of transitions. | |
object Lab { | |
/** ************** Types */ | |
trait StateDef { | |
def id: String | |
} | |
case class State[CV](override val id: String, context: CV) extends StateDef | |
trait Action[P, R] | |
abstract class Condition[-T] extends Function1[T, Boolean] { | |
override def apply(contextState: T): Boolean | |
} | |
case class Transition[P, R](tailState: StateDef, headState: StateDef, action: Action[P, R], condition: Option[Condition[P]] = None) | |
case class Workflow private(transitions: List[Transition[P, R] forSome {type P; type R}]) { | |
def getTransitions[V](tail: StateDef, head: StateDef): List[Transition[P, R] forSome {type P >: V; type R}] = { | |
transitions.filter(t => true).map(t => t.asInstanceOf[Transition[V, _]]) | |
} | |
def matchTransition[V](tail: State[V], head: StateDef): Option[Transition[P, R] forSome {type P >: V; type R}] = { | |
val value = tail.context | |
val transitions = getTransitions[V](tail, head) | |
transitions.find(t => t.condition.forall(cond => cond(value))) | |
} | |
} | |
/** ************** Fixtures */ | |
// Model | |
case class CreateImage() | |
case class Image() | |
// States | |
class Init extends State[CreateImage]("INIT", CreateImage()) | |
val init = new Init() | |
case object Published extends StateDef { | |
override def id: String = "PUBLISHED" | |
} | |
// Action | |
class CreateTipAction extends Action[CreateImage, Image] | |
/** ************** Demo */ | |
val transitions = List( | |
Transition(init, Published, new CreateTipAction()) | |
) | |
val w = Workflow(transitions) | |
val t = w.matchTransition(init, Published) | |
} |
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