Here is the latest blog post by Bertrand Meyer.
http://bertrandmeyer.com/2011/07/04/if-im-not-pure-at-least-my-functions-are/It talks about the problem of function purity and broaches the subject of framing. In short, the frame of the specification of a routine is the set of variables (in the broad meaning of the term) that the execution of the routine can modify. In object oriented programming, it is especially tricky because of the sets of dynamically allocated objects of which it might be necessary to alter the state in a given routine. Indeed such set can be taken to be the set of objects reachable from a given root. In a limited solution, such as shown by Meyer in his latest post, you only name variables and expressions that can change. In more elaborate solutions, such as the dynamic frames of Kassios (as quoted by Meyer), it is possible to provide a set of objects and the attributes that can be expected to change. It is especially handy for specifying dynamic data structures like linked lists.
Such a solution seems to present the disadvantage of disallowing the extension of frames through inheritance, which Meyer preserves. I think a compromise can be reached between the two but it is a bit too involved for a post only intended for sharing another blog post.
