access modifiers - What are the differences between final class and sealed class in Scala? -

there 2 types of modifiers in scala: final , sealed

what differences between them? when should use 1 on other?

a final class cannot extended, period.

a sealed trait can extended in same source file it's declared. useful creating adts (algebraic data types). adt defined sum of derived types.

e.g.:

sealed trait option[+a]  final case class some[+a] extends option[a] object none extends option[nothing]

because option[a] sealed, cannot extended other developers - doing alter meaning.

some[a] final because cannot extended, period.

as added bonus, if trait sealed, compiler can warn if pattern matches not exhaustive enough because knows option limited some , none.

opt match {     case some(a) => "hello" }

warning: match may not exhaustive. fail on following input: none

Premier