Enum in Ruby

enum.rb

# Slightly odd to inherit from Module; this lets us define consts such as FOOBAR::FOO
class Enum < Module
  include Enumerable

  attr_reader :values

  delegate :each, to: :values

  def initialize(&blk)
    super(&nil) # Don't pass the block to super
    @values = Set.new
    # Define an EnumSet by passing a block to `new` with calls to `value`
    instance_eval(&blk)
    # Once the values are defined, we don't want the set to be modified.
    @values.freeze
  end

  # Called during initialization to add values to the EnumSet
  # After initialize, the set will be frozen, so you cannot call this afterwards.
  def value(name, value = name)
    const_set(name, value)
    @values << value
  end
end

x_enum.md

EnumSet: define a quick enum instance with named consts

Usage: initialize a new EnumSet, passing a block declaring values:

FOOBAR = EnumSet.new do
  value "FOO"
  value "BAR"
end

This restuls in

FOOBAR::FOO -> "FOO"
FOOBAR::BAR -> "BAR"
FOOBAR.values -> ["FOO", "BAR"]

The returned intance is also an Enumerable, so you can iteratre on it directly using each, map, select, and so on.

All values must be valid const names.

If you wish to use values that differ from the names, simply use a second argument

FOOBAR = EnumSet.new do
  value "FOO", "foo"
  value "BAR", "wahoo"
end

This restuls in

FOOBAR::FOO -> "foo"
FOOBAR::BAR -> "wahoo"
FOOBAR.values -> ["FOO", "BAR"]