Scala Language Partial Functions Composition
Example
Partial functions are often used to define a total function in parts:
sealed trait SuperType
case object A extends SuperType
case object B extends SuperType
case object C extends SuperType
val pfA: PartialFunction[SuperType, Int] = {
case A => 5
}
val pfB: PartialFunction[SuperType, Int] = {
case B => 10
}
val input: Seq[SuperType] = Seq(A, B, C)
input.map(pfA orElse pfB orElse {
case _ => 15
}) // Seq(5, 10, 15)
In this usage, the partial functions are attempted in order of concatenation with the orElse method. Typically, a final partial function is provided that matches all remaining cases. Collectively, the combination of these functions acts as a total function.
This pattern is typically used to separate concerns where a function may effectively act a dispatcher for disparate code paths. This is common, for example, in the receive method of an Akka Actor.
