enum.rb

require 'set'

class I18n
  def self.t(t, options = {})
    "#{t} - #{options}"
  end
end

class Enum
  class TokenNotFoundError < StandardError; end

  class << self
    def inherited(child)
      return if self == Enum

      child.__values__ = self.__values__.clone
    end

    def values(*ary)
      ary.each { |val| __values__.add(val.to_s) }
    end

    def all
      __values__
    end

    def token(t)
      ts = t.to_s
      unless __values__.include?(ts)
        raise(TokenNotFoundError, "token '#{t}'' not found in the enum #{self}")
      end
      ts
    end

    def name(t)
      translate(token(t))
    end

    protected

    def __values__
      @__values__ ||= Set.new
    end

    def __values__=(set)
      @__values__ = set
    end

    private

    def translate(token)
      I18n.t(token, scope: "enum.#{self}")
    end
  end
end


class Side < Enum
  values :left, :right, :whole
end

class SSide < Side
  values :sleft
end

class T < Enum
  values :a
end


puts T.all.to_a.inspect

puts Side.token(:left)
puts Side.token('right')
puts (begin Side.token(:invalid); rescue Enum::TokenNotFoundError => e; 'invalid'; end)
puts Side.all.to_a.inspect
puts Side.name(:left)
puts (begin Side.name(:invalid); rescue Enum::TokenNotFoundError => e; 'invalid'; end)

puts SSide.all.to_a.inspect

__END__
left
right
invalid
["left", "right", "whole"]
left - {:scope=>"enum.Class"}
invalid
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