Re: [boost] Re: Re: is_base_and_derived question

From: Terje Slettebø (tslettebo_at_[hidden])
Date: 2003-01-30 10:40:44

>From: "John Maddock" <jm_at_[hidden]>

> >This is tested on Comeau 4.3,  Intel C++ 6/7 and g++ 3.2.
>
> Except it *doesn't work* !
>
> The problem is that your static assertion don't test anything, changing
to:
>
> //typedef char TestA[is_base_and_derived<B, D>::result]; // Multiple bases
> (error on g++)
> typedef char TestB[is_base_and_derived<B1,D>::result ? 1 : -1];
> //typedef char TestC[is_base_and_derived<B2,D>::result]; // Private base
> (error on g++)
> typedef char TestD[!is_base_and_derived<int,D>::result ? 1 : -1];
> typedef char TestE[!is_base_and_derived<B, B>::result ? 1 : -1];
> typedef char TestF[is_base_and_derived<B,DV>::result ? 1 : -1]; // Virtual
> base
>
> and both Borland and gcc 3.21 give errors on cases 2 and 6

Well, this means that there are other problems in these compilers. The
following _should_ give an error:

typedef char Test[0];

and indeed it does on the EDG compilers.

Well, then it turns out that even this version doesn't work correctly on g++
and Borland, and it doesn't give an error, either, for the above cases.
Using BOOST_STATIC_ASSERT, this would have been detected.

There's no need to shout. :) The test code should work on a conforming
compiler.

By the way, those "static asserts" were "inherited" from Rani's example
code, with a couple of additions. I guess this is a good reason to use a
portable static assert, like the Boost one.

Regards,

Terje