Scala 3 Enum vs Enumerations

[noahehall]

Whats the difference between a scala Enum vs a scala Enumeration?

Also, I could find Enumeration in the scala 3 ref (Enumeration)

but I couldnt find Enum: does anyone have a link?

• I did find this explanation: Enumerations

[BalmungSan]

Enumeration exists since Scala 2 and it’s a mistake, never ever use it.

enum is a keyword added in Scala 3 that is just sugar syntax for a common pattern in Scala 2 to define ADTs (and thus enums) using sealed traits and case classes / objects

[philipschwarz]

The above are from Scala 3 by Example - Algebraic Data Types for Domain Driven Design - …

[halloleo]

@BalmungSan

Enumeration exists since Scala 2 and it’s a mistake, never ever use it.

Thanks for this clear advice!

[andreak]

@BalmungSan

enum is a keyword added in Scala 3 that is just sugar syntax

To clarify: It’s not just that, it also generates Java-compatible Enums, which is handy working with java-libs.

[adamdabrowski]

Here’s some background on Scala’s Enumeration: enums - Using Enumerations in Scala Best Practices - Stack Overflow

[BalmungSan]

@andreak

it also generates Java-compatible Enums

Uhm my definition of sugar syntax is that it just generates different code than what you see.
Making them Java enums is just a matter of extending an interface IIRC.

Unless your point was that I missed mentioning that. Which then fair, thanks for the addition.
I just don’t consider that to be a good feature either but that is another discussion.

[Jasper-M]

@BalmungSan

Uhm my definition of sugar syntax is that it just generates different code than what you see.

IIUC you can’t write a real java compatible enum in “regular” scala code. At the very least because there needs to be a special flag enabled in the class file, but possibly it also requires other inexpressible constructs. So in that sense it is more than syntax sugar.

[BalmungSan]

@Jasper-M

IIUC you can’t write a real java compatible enum in “regular” scala code.

Uhm is that so? My understanding was that all you needed was to extend an interface but I may be wrong in that.
If so, yeah is more than syntax.

Although, again, I don’t think it doing that by default is a good feature.

[som-snytt]

This is a scary diagnostic:

An exception has occurred in the compiler (21.0.2). Please file a bug against the Java compiler via the Java bug reporting page (https://bugreport.java.com) after checking the Bug Database (https://bugs.java.com) for duplicates. Include your program, the following diagnostic, and the parameters passed to the Java compiler in your report. Thank you.
com.sun.tools.javac.code.Symbol$CompletionFailure: class file for scala.reflect.Enum not found

but putting it on the class path works.

-cp ".sdkman/candidates/scala/3.4.0/lib/*"

I needed this exercise in recalling Java syntax.

public class Colorized {
        public Color test(Color c) {
                switch (c) {
                        case Red: return Color.Green;
                        default: return Color.Blue;
                }
        }
}

where

enum Color extends Enum[Color]:
  case Red, Green, Blue

I’m not motivated to try advanced features, but javap says ACC_ENUM everywhere.

Also Scala 3: Enum vs Enumerations is my favorite monster movie sequel.

It’s the rare monster movie where instead of Tokyo they devastate the shores of Lake Geneva.

[spamegg1]

Here’s a short demonstration of Scala 3 Enum Java interop (towards the end of the video): https://www.youtube.com/watch?v=YlVVhLvN71Y