class Hash
  # Returns a new hash with +self+ and +other_hash+ merged recursively.
  def deep_merge(other_hash)
    merge(other_hash) do |key, oldval, newval|
      oldval = oldval.to_hash if oldval.respond_to?(:to_hash)
      newval = newval.to_hash if newval.respond_to?(:to_hash)
      oldval.is_a?( Hash ) && newval.is_a?( Hash ) ? oldval.deep_merge(newval) : newval
    end
  end

  # Returns a new hash with +self+ and +other_hash+ merged recursively.
  # Modifies the receiver in place.
  def deep_merge!(other_hash)
    replace(deep_merge(other_hash))
  end
end