Ruby Enum type

enum.rb

class Enum
  attr_reader :name
  attr_reader :value

  def initialize(name, value)
    @name = name
    @value = value
  end

  def to_i
    value.to_i
  end

  def to_sym
    name.to_sym
  end

  def to_s
    "<#{self.class.name}::#{name} value=#{value}>"
  end
  
  class << self
    def enum_value(name, value)
      @@values ||= []

      raise 'Name already exists' if @@values.detect { |item| item.name == name }
      raise 'Value already exists' if @@values.detect { |item| item.value == value }

      new_value = new(name, value)
      @@values << new_value

      const_set(name, new_value)
    end

    def values
      @@values ||= []
    end

    private

    def new(*args)
      super
    end
  end
end

example.rb

class Country < Enum
  enum_value :RUSSIA, 1
  enum_value :USA, 2
end

puts Country::RUSSIA              # <Country::RUSSIA value=1>
p Country::RUSSIA.is_a?(Country)  # true

p Country.values

country1 = Country::RUSSIA
country2 = Country::RUSSIA
p country1 == country2            # true


# Errors

class Country < Enum
  enum_value :RUSSIA, 1
  enum_value :RUSSIA, 2           # raise
end

class Country < Enum
  enum_value :RUSSIA, 1
  enum_value :USA, 1              # raise
end

Country.new(:China, 3)            # raise