Include this module into a DataMapper model to enable multiparameter attributes.

A multiparameter attribute has +attr(Xc)+ as name where attr specifies the attribute, X the position of the value, and c an optional typecast identifier. All values that share an attr are sorted by their position, optionally cast using +to_c+ (where c is the typecast identifier) and then used to instantiate the proper attribute value.

@example

  # Assigning a hash with multiparameter values for a +Date+ property called
  # +written_on+:
  resource.attributes = {
      'written_on(1i)' => '2004',
      'written_on(2i)' => '6',
      'written_on(3i)' => '24' }

  # +Date+ will be initialized with each string cast to a number using
  # #to_i.
  resource.written_on == Date.new(2004, 6, 24)