[Exceptional C++ Style] Item 18 - Virtuality

[Balog Pal]

> One of my questions concerning NVI is precisely the question of 
> appropriateness. I have been looking for an appropriate context for many 
> years, and have to find a solidly convincing one. As a problem-solving 
> design it seems somewhat speculative.

I recall James Kanze writes his stuff DBC style and uses NVI like this.
There functions are really close to TM, as the fuctions actually does check 
invariants, preconditions, postconditions around the do-work stuff.