Re: How to debug method resolution problem?

From:

Yu Han <hanjunyu@163.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 10 Feb 2010 23:06:27 +0800

Message-ID:

<hkuiaq$1q6t$1@adenine.netfront.net>

May be you could declare A::foo as pure virtual. But I guess you do have
something useful in A::foo, so you have to do something different.
Following is a solution that partially solve your problem:

On 02/10/2010 10:02 PM, jburgy wrote:

Good morning,

I'm faced with a tricky problem and the C++ gurus I work with couldn't
help. I apologize for not posting actual code, I simply can't for IP
reasons. I have the following inheritance diagram:

class A
{
virtual A *foo( ... ) const;
};

template< class T>
class B : public A
{
virtual A *foo( ... ) const;

      private:
        // add a pure virtual function
        virtual A* bar( ... ) const = 0;

};

then compiler would give you a error for auto instantiation of B.
But for specializations by yourself you must to give a definition for
bar and, just call it from foo.

The problem is that if you do not provide a foo definition for B's
template specialization, you still get no errors at compile time. Since
it would get one from A.

template< class T>
inline A *B::foo( ... ) const
{
throw( "B's template specializations must override foo!" );
return NULL;
}

I have specializations of B for 8 distinct classes T. I have
explicitly overridden foo for all of them (using a preprocessor macro)
but am getting mixed results. Some cases still end up throwing the
error message shown above (3 when building with MSVC and 5 with g++
although I have no compile errors in either case). Is this something
that's not supported by the standard and I shouldn't expect it to work
reliably? How do I go about debugging it since the problem occurs at
compile-time.

Thanks,

--
Yu Han

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