python-scala-sealed-enum

Python Enum → Scala Sealed Traits

Python Pattern

class TokenType(Enum):
    STRING = "string"
    NUMERIC = "numeric"
    NULL = "null"

Scala Idiomatic Translation

Use sealed abstract class (not Enum) with a companion object holding case object members:

sealed abstract class TokenType(val value: String)

object TokenType {
  case object STRING  extends TokenType("string")
  case object NUMERIC extends TokenType("numeric")
  case object NULL    extends TokenType("null")
}

Why sealed abstract class over sealed trait?

• Use sealed abstract class when members need constructor parameters (like value: String).
• Use sealed trait for purely marker/tag types with no data.

Key Differences from Python

Python	Scala
TokenType.STRING.value	TokenType.STRING.value (same API)
isinstance(x, TokenType)	Pattern match on sealed type
Can iterate list(TokenType)	Use Set(STRING, NUMERIC, ...) manually
TokenType["STRING"]	Not needed; use TokenType.STRING directly

Exhaustive Pattern Matching (Bonus)

def describe(t: TokenType): String = t match {
  case TokenType.STRING  => "A string token"
  case TokenType.NUMERIC => "A numeric token"
  case TokenType.NULL    => "A null token"
  // Compiler warns if a case is missing (because sealed)
}

Companion Object values List (if needed)

object TokenType {
  case object STRING  extends TokenType("string")
  case object NUMERIC extends TokenType("numeric")
  case object NULL    extends TokenType("null")

  val values: List[TokenType] = List(STRING, NUMERIC, NULL)

  def fromString(s: String): Option[TokenType] =
    values.find(_.value == s)
}