A very interesting and important question frequently is, what effect has been produced upon a right of action, or upon a previously existing defence to an action, by a change in the law effected by statute after the right has accrued, or the cause of action has arisen, to which the defence was applicable. The question is encountered in a great variety of cases, and is sufficiently important to be considered under the several heads where the cases seem to range themselves. This is done imperfectly below.
Cooley, Thomas M. "Effect of a Change in the Law Upon Rights of Actions and Defences." Southern L. Rev. 3 (1877): 33-49.