Case objects vs Enumerations in Scala

Question

Are there any best-practice guidelines on when to use case classes (or case objects) vs extending Enumeration in Scala?

They seem to offer some of the same benefits.

Answer 1

Update March 2017: as commented by Anthony Accioly, the scala.Enumeration/enum PR has been closed.

Dotty (next generation compiler for Scala) will take the lead, though dotty issue 1970 and Martin Odersky's PR 1958.

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Note: there is now (August 2016, 6+ years later) a proposal to remove scala.Enumeration: PR 5352

Deprecate scala.Enumeration, add @enum annotation

The syntax

@enum
 class Toggle {
  ON
  OFF
 }

is a possible implementation example, intention is to also support ADTs that conform to certain restrictions (no nesting, recursion or varying constructor parameters), e. g.:

@enum
sealed trait Toggle
case object ON  extends Toggle
case object OFF extends Toggle

Deprecates the unmitigated disaster that is scala.Enumeration.

Advantages of @enum over scala.Enumeration:

• Actually works
• Java interop
• No erasure issues
• No confusing mini-DSL to learn when defining enumerations

Disadvantages: None.

This addresses the issue of not being able to have one codebase that supports Scala-JVM, Scala.js and Scala-Native (Java source code not supported on Scala.js/Scala-Native, Scala source code not able to define enums that are accepted by existing APIs on Scala-JVM).