multi_parameter_support.rb

# a slightly modified version of multi-parameter attribute support
# extracted from ActiveRecord::Base for use with non-ActiveRecord classes

module MultiParameterSupport
  def assign_multiparameter_attributes(pairs)
    extract_callstack_for_multiparameter_attributes(pairs).each do |name, values|
      send("#{name}_with_multiparameter_assignment=", *values)
    end
  end

  # this is just extracted directly from ActiveRecord::Base
  def extract_callstack_for_multiparameter_attributes(pairs)
    attributes = { }

    for pair in pairs
      multiparameter_name, value = pair
      attribute_name = multiparameter_name.split("(").first
      attributes[attribute_name] = [] unless attributes.include?(attribute_name)

      unless value.empty?
        attributes[attribute_name] <<
          [ find_parameter_position(multiparameter_name), type_cast_attribute_value(multiparameter_name, value) ]
      end
    end

    attributes.each { |name, values| attributes[name] = values.sort_by{ |v| v.first }.collect { |v| v.last } }
  end

  def type_cast_attribute_value(multiparameter_name, value)
    multiparameter_name =~ /\([0-9]*([if])\)/ ? value.send("to_" + $1) : value
  end

  def find_parameter_position(multiparameter_name)
    multiparameter_name.scan(/\(([0-9]*).*\)/).first.first
  end
end

my_class.rb

# You still need to implement the accessors manually as there is none of ActiveRecord's reflection-fu.

class MyClass
  include MultiParameterSupport

  attr_accessor :start_date

  def start_date_with_multiparameter_assignment=(*args)
    self.start_date = Date.new(*args)
  end
end