Enum Extensions

The Enum Extensions library provides type classes to work generically with enumerations in Scala 3

Usage

Type classes are provided in the enumextensions package.

Enum Mirror

EnumMirror[E] is a type class that provides reflection over an enumeration type E. It provides several capabilities:

• cached values as an IArray[E]
• reflection of name (String) or ordinal (Int) for any individual case.
• safe lookup individual cases by name or ordinal,
• unsafe (efficient) lookup of individual cases by name or ordinal.

See the above use cases in action below:

import enumextensions.EnumMirror

def enumName[E: EnumMirror]: String =
  EnumMirror[E].mirroredName // e.g. example.Color

def sortedCases[E: EnumMirror]: IArray[E] =
  EnumMirror[E].values // cached IArray

def nameOrdinalPairs[E: EnumMirror]: Map[String, Int] =
  Map.from( //                      ┌ NAME    ┌ ORDINAL
    for e <- sortedCases[E] yield e.name -> e.ordinal
  )

// Lookups returning `Option[E]`
def safeLookup[E: EnumMirror](name: String): Option[E] =
  EnumMirror[E].valueOf(name)
def safeLookup[E: EnumMirror](ordinal: Int): Option[E] =
  EnumMirror[E].fromOrdinal(ordinal)

// assert that name/ordinal exists for convenience
def unsafeLookup[E: EnumMirror](name: String): E =
  EnumMirror[E].valueOfUnsafe(name)
def unsafeLookup[E: EnumMirror](ordinal: Int): E =
  EnumMirror[E].fromOrdinalUnsafe(ordinal)

given instances of EnumMirror are not provided automatically, you must explicitly opt in as follows:

enum Color derives EnumMirror:
  case Red, Green, Blue

Numeric

In the enumextensions.numeric package we provide NumericOps, which extends types with a given EnumMirror[E] into a given scala.math.Integral[E], as well as providing standard numeric operations over the enum, it is simple to create sub-ranges of values.

Let's define a WeekDays enumeration, opting into numeric derivation by derives NumericOps, and declare ranges for both the daysOfWeek and weekend:

import enumextensions.EnumMirror
import enumextensions.numeric.NumericOps

enum WeekDays derives EnumMirror, NumericOps:
  case Monday, Tuesday, Wednesday, Thursday, Friday
  case Saturday, Sunday

object WeekDays:
  val daysOfWeek = Monday to Friday
  val weekend    = Saturday to Sunday

here is a demonstration of using the numeric operators, e.g.

scala> -(-Wednesday) == Wednesday
true