name.rb

class Name
  def initialize name=''
    @name = name
  end

  def name
    @name ||= @name.to_s
  end
  alias :full :name

  def first
    split_name.first
  end

  def last
    split_name.last
  end

  def == other
    self.to_s == other.to_s
  end

  def to_s
    name
  end

  def inspect
    "#<Name \"#{name}\">"
  end

private

  def split_name
    @split_name ||= name.split ' ', 2
  end
end

user.rb

class User < ActiveRecord::Base
  def name
    @name ||= Name.new super
  end

  def name= new_name
    @name = Name.new new_name
    super @name
  end

  def first_name
    name.first
  end

  def last_name
    name.last
  end
end

User has a name column that is a string.