
class Hash

  # Allows for reverse merging where its the keys in the
  # calling hash that wins over those in the <tt>other_hash</tt>.
  # This is particularly useful for initializing an incoming
  # option hash with default values:
  #
  #   def setup(options = {})
  #     options.reverse_merge! :size => 25, :velocity => 10
  #   end
  #
  # The default :size and :velocity is only set if the +options+
  # passed in doesn't already have those keys set.

  def reverse_merge(other_hash)
    other_hash.merge(self)
  end

  def reverse_merge!(other_hash)
    replace(reverse_merge(other_hash))
  end

  alias_method :reverse_update, :reverse_merge!
end
