How to understand FAQ 24.4

[thomas]

link: http://www.parashift.com/c++-faq-lite/private-inheritance.html#faq-24.4

There's a sentence:

"However users of PrivatelyDer should avoid this unsafe conversion,
since it is based on a private decision of PrivatelyDer, and is
subject to change without notice. "

Does it mean that PrivatelyDer decides to make the base class private,
so users should not publicly use a base pointer? Because private
inheritance intends the hide of base class, the use of Base type
pointer should be avoided.

 

[James Kanze]

link:http://www.parashift.com/c++-faq-lite/private-inheritance.html#faq-24.4

There's a sentence:

"However users of PrivatelyDer should avoid this unsafe conversion,
since it is based on a private decision of PrivatelyDer, and is
subject to change without notice. "

Does it mean that PrivatelyDer decides to make the base class private,
so users should not publicly use a base pointer? Because private
inheritance intends the hide of base class, the use of Base type
pointer should be avoided.

It means that private inheritance, like anything else private,
is an implementation detail, not part of the contract, and the
client code shouldn't count on it; the authors of client code
should, in fact, code as if it didn't exist, or at least as if
they don't know of its existance.