Merging two ruby objects

Question: Is there a concise way in Ruby (and/or Rails) to merge two objects together?

Specifically, I'm trying to figure out something akin to jQuery's $.extend() method, whereas the first object you pass in will have its properties overridden by the second object.

I'm working with a tableless model in Rails 3.2+. When a form submission occurs, the parameters from the submission are used to dynamically populate a User object. That user object is persisted between page requests using Ruby's PStore class, marshalling objects to flat files which can be easily retrieved in the future.

Relevant code:

module Itc
  class User
    include ActiveModel::Validations
    include ActiveModel::Conversion
    include ActionView::Helpers
    extend ActiveModel::Naming

    def set_properties( properties = {} )
      properties.each { |k, v|
        class_eval("attr_reader :#{k.to_sym}")
        self.instance_variable_set("@#{k}", v)
      } unless properties.nil?
    end
  end
end

Creation of a user object occurs like this:

user = Itc.User.new( params[:user] )
user.save()

The save() method above is not ActiveRecord's save method, but a method I wrote to do persistence via PStore.

If I have a user object loaded, and I have a form submission, I'd like to do something like this:

merged = existingUserObject.merge(User.new(params[:user])

and have the outcome of merged be a user object, with only properties that were changed in the form submission be updated.

If anyone has any ideas about a better way to do this in general, I'm all ears.