Re: [boost] Re: additional test for is_abstract type trait

From: John Maddock (john_at_[hidden])
Date: 2004-11-16 11:27:31

> 1) a corrected version of is_abstract_template_test.cpp
>
>   When I prepared the original version I did not realize that
>   is_abstract<T&>::value is supposed to be false for any type T.
>
> 2) a patch to boost/type_traits/is_abstract.hpp that works around gcc
>   bug #17232.
>
>   I would not be surprised if my patch turns out to be overly
>   complicated. I had assumed that any expression that involves
>   sizeof(T) causes the instantiation of T if T is a template
>   specialization. So I tried, e.g., to add the condition
>   sizeof(T) > 0 to the parameter list of ice_and in is_abstract_imp.
>   For some reason, though, whatever I tried showed no effect.
>   (Perhaps the compiler realized that the conditions I added were
>   true for any type T and eliminated the evaluation of sizeof(T)?)
>
>   I finally settled for attached patch that adds a further struct in
>   which SFINAE is used again.
>
> With this patch gcc 3.4.2 passes both is_abstract_test.cpp as well as
> the attached is_abstract_template_test.cpp.
>
> I still would like to see something like is_abstract_template_test.cpp
> added to the type_traits tests. It is easy to introduce subtle bugs
> both in the compiler when implementing SFINAE and template
> instantiation as well as in the code relying on SFINAE.

I agree, sorry for not getting on top of this, but I will add your tests 
into the type traits test suite at some point (and the patch as well 
obviously).

Thanks for this,

John.