Jonathan M Davis wrote:
It would not be good to be unable to do NVI.
I am not saying that it should not be supported; but...
I've used NVI a number of times myself until I was convinced by Kevlin
Henney that it was "a solution in search of a problem" during one of his
many excellent presentations at the Silicon Valley ACCU:
http://www.accu-usa.org/Slides/ACriticalViewOfCppPractices.pdf
A couple of slides can't convey his thoughts, but here they are:
<quote slide="27">
Non-virtual Interfaces?
NVI suggests virtuals should be private and wrapped in public
non-virtuals
Over the last decade or so this has been proposed by some as a
good practice guideline
It has structural similarities with Template Method, but has a
distinct form and (in)distinct motivation
However, it is a solution in search of a problem
On close inspection the problems it purports to resolve are
better addressed by other more mature and proven techniques,
e.g. the Interceptor pattern
</quote>
<quote slide="28">
Non-Valuable Idiom
NVI lacks either a clear motivation or a clear description of
benefits
Motivation is often presented in terms of shotgun speculation —
code simplification, instrumentation, extensibility, decoupling,
thread safety, assertion checking, etc. — that does not stand up
to scrutiny
NVI singularly fails to adequately offer the benefits that are
advertised as its motivation
In practice it is a somewhat tedious and verbose technique that
adds baggage to a class hierarchy
</quote>
Ali
