Re: Why can't call a base member function from a object of sub class???

From:

"Alf P. Steinbach" <alfps@start.no>

Newsgroups:

comp.lang.c++

Date:

Tue, 17 Feb 2009 04:19:08 +0100

Message-ID:

<gndabg$5jb$1@reader.motzarella.org>

* Albright:

On Feb 17, 10:37 am, "Alf P. Steinbach" <al...@start.no> wrote:

This is a FAQ (Frequently Asked Question).

See the FAQ item titled "What's the meaning of, Warning: Derived::f(char) hides
Base::f(double)?", currently item 23.9 and available at e.g. <url:http://www.parashift.com/c++-faq-lite/strange-inheritance.html#faq-23.9>, plus
at a host of mirror sites.

It's often a good idea to check the FAQ.

But Why the C++ standard has this rule?

Hm, properly that question belongs in [comp.std.c++]; here in [comp.lang.c++] we
mostly only deal with the language as-is.

However...

If C++ didn't have this rule it would have to have the opposite rule, at least
for this case, i.e. no hiding. That would be a different trade-off with its own
problems. For example, in that case adding a name in a base class could silently
(or more visibly) affect code using an existing derived class, requiring fixing
all the derived classes -- pretty hopeless when your class is in a library
used by many, and the classes to be fixed are the many's derived classes.

The rule that was adopted avoids e.g. that problem, at the cost of that rule
being somewhat counter intuitive, and generating a Frequently Asked Question.

A good textbook should explain this, but I don't know whether they do.

Cheers & hth.,

- Alf

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