2.3 Enum Instance

Haxe provides powerful enumeration (short: enum) types, which are actually an algebraic data type (ADT). While they cannot have any expressions, they are very useful for describing data structures:

enum Color {
  Rgb(r:Int, g:Int, b:Int);

Semantically, this enum describes a color which is either red, green, blue or a specified RGB value. The syntactic structure is as follows:

  • The keyword enum denotes that we are declaring an enum.
  • Color is the name of the enum and could be anything conforming to the rules for type identifiers.
  • Enclosed in curly braces {} are the enum constructors,
  • which are Red, Green, and Blue taking no arguments,
  • as well as Rgb taking three Int arguments named r, g and b.

The Haxe type system provides a type which unifies with all enum types:

Define: Enum<T>

This type is compatible with all enum types. At compile-time, Enum<T> can be seen as the common base type of all enum types. However, this relation is not reflected in generated code.