Optional class in Ruby

optional.rb

class Optional
  private_class_method :new

  class << self
    def some(value)
      new(value, false)
    end

    def none
      new(nil, true)
    end
  end

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

  def some?
    !none?
  end

  def none?
    @is_none
  end

  def get
    some? ? @value : raise(NoneHasNoValue)
  end

  def get_or_else(default_value)
    some? ? @value : default_value
  end

  def map(&_block)
    return self unless block_given?

    if some?
      self.class.some(yield @value)
    else
      self
    end
  end

  class NoneHasNoValue < StandardError; end
end