data_wrapper.rb

class DataWrapper
  def initialize(data_hash)
    raise ArgumentError unless data_hash.is_a? Hash
    @data_hash = data_hash
  end

  def add(name, value)
    DataWrapper.new(data_hash.merge({ name.to_sym => value }))
  end

  def to_hash
    data_hash
  end

  private; attr_reader :data_hash
end