This is a little module that simulates enumerated types in Lua.

Its API is very similar to the Python3 Enum API, although much more limited.

enum = require("enum")

sizes = {"SMALL", "MEDIUM", "BIG"}
Size = enum.new("Size", sizes)
print(Size) -- "<enum 'Size'>"
print(Size.SMALL) -- "<Size.SMALL: 1>"
print(Size.SMALL.name) -- "SMALL"
print(Size.SMALL.value) -- 1
assert(Size.SMALL ~= Size.BIG) -- true
assert(Size.SMALL < Size.BIG) -- error "Unsupported operation"
assert(Size[1] == Size.SMALL) -- true
Size[5] -- error "Invalid enum member: 5"

-- Enums cannot be modified
Size.MINI -- error "Invalid enum: MINI"
assert(Size.BIG.something == nil) -- true
Size.MEDIUM.other = 1 -- error "Cannot set fields in enum value"

-- Keys cannot be reused
Color = enum.new("Color", {"RED", "RED"}) -- error "Attempted to reuse key: 'RED'"

If you are on NixOS, you can install this package from nix-stefano-m-overlays.

This package can be installed as a nix flake. It provides packages for the various versions of Lua shipped with nix as well as an overlay that adds the enum attribute to the Lua package sets.

NOTE

To ensure that the flake overlays are composable, enum is added directly to the top-level luaPackages. An unfortunate consequence is that enum will not be present in lua.pkgs. To use enum in lua.withPackages, one must refer to the top-level luaPackages.

For example, say that you want a Lua environment with enum and http, you need to do something like:

let
  # assume that enumOverlay is the overlay provided by the enum flake.
  pkgs = import <nixpkgs> {overlays = [enumOverlay];};
in
# http is present in lua.pkgs
# enum is not present in lua.pkgs
myLuaEnv = pkgs.lua.withPackages(ps: [ps.http pkgs.luaPackages.enum])

This package is published to Luarocks as enum and can be installed using

luarocks install enum