More meaningful ActiveRecord::Enum

enum1.rb

class Enum
  def self.value(key, value = nil)
    @enum ||= {}
    @enum[key] = value || @enum.size
    define_singleton_method(key) { @enum[key] }
  end

  def self.enum
    @enum
  end
end

class Gender < Enum
  value :undefined
  value :male
  value :female
end

class User < ActiveRecord::Base
  enum gender: Gender.enum
end

User.new(gender: Gender.male)

enum2.rb

class Enum
  def self.create(*args)
    Class.new do
      @enum = {}
      define_singleton_method(:enum) { @enum }
      args.each do |key|
        @enum[key] = @enum.size
        define_singleton_method(key) { @enum[key] }
      end
    end
  end
end

Gender = Enum.create(:undefined, :male, :female)

class User < ActiveRecord::Base
  enum gender: Gender.enum
end

User.new(gender: Gender.male)

enum3.rb

class Enum
  def self.new(*args, **kwargs)
    Class.new do
      @enum = Hash[args.each_with_index.to_a].merge(kwargs || {}).freeze
      @enum.each { |key, value| define_singleton_method(key) { value } }
      define_singleton_method(:enum) { @enum }
    end
  end
end

Gender = Enum.new(undefined: 0, male: 1, female: 2)

class User < ActiveRecord::Base
  enum gender: Gender.enum
end

User.new(gender: Gender.male)