def validates_exclusion_of(*attr_names)
configuration = { :message => ActiveRecord::Errors.default_error_messages[:exclusion], :on => :save }
configuration.update(attr_names.extract_options!)
enum = configuration[:in] || configuration[:within]
raise(ArgumentError, "An object with the method include? is required must be supplied as the :in option of the configuration hash") unless enum.respond_to?("include?")
validates_each(attr_names, configuration) do |record, attr_name, value|
record.errors.add(attr_name, configuration[:message] % value) if enum.include?(value)
end
end