The ideas are closely related, and so are the implementations, but my code really had nothing to do with pre/post processing. The purpose of the tied interface was to wedge the test into all mutators applied to the lvalue accessor sub. Hence the test is done in STORE().

The Constraint tie interface class written for that is really independent of lexical closures and lvalue subs. It could be applied directly to package globals or any other sort of scalar variable. The choice of die as an error reporting mechanism was from the "die is throw, eval is try" school of thought. I didn't want to muck up current values on bad assignments by returning undef or whatever.

One implementation of pre/post processing is done in TheDamian's Hook::LexWrap, a highly mystical module. I don't know if subs wrapped by that module can be lvalues, but I think I will have a good time finding out this evening :-)