def merge!(other)
  other = Rubinius::Type.coerce_to other, Hash, :to_hash

  if block_given?
    other.each_entry do |entry|
      key = entry.key
      if key? key
        __store__ key, yield(key, self[key], entry.value)
      else
        __store__ key, entry.value
      end
    end
  else
    other.each_entry do |entry|
      key = entry.key
      __store__ key, entry.value
    end
  end
  self
end