class Hash
  # Returns a new hash with +self+ and +other_hash+ merged recursively.
  def deep_merge(other_hash)
    dup.deep_merge!(other_hash)
  end

  # Returns a new hash with +self+ and +other_hash+ merged recursively.
  # Modifies the receiver in place.
  def deep_merge!(other_hash)
    other_hash.each_pair do |k,v|
      tv = self[k]
      self[k] = tv.is_a?(Hash) && v.is_a?(Hash) ? tv.deep_merge(v) : v
    end
    self
  end
end