Maybe there's something out there that implements something akin to Lisp's :after methods in Perl that would do what you want.
Well, there is Hook::LexWrap. But if what I read elsewhere in this thread is true (that we assume the computation of 'C' is expensive and we'd like to cache it), then you'd just want to clear the 'C' cache when you change 'A' or 'B', and when you request 'C', just return the cached value if it exists, else compute, cache, and return it.

In reply to Re: semi-OT: Lisp code by runrig
in thread OO, Class::MethodMaker, and get_set by sigma

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