Re: [boost] Can type_traits be user specialized?

From: John Maddock (jm_at_[hidden])
Date: 2002-11-15 06:40:19

> I have a problem however, which I think it would be useful to discuss
> generally.
>
> Unfortunately, some compilers -like bcc55- provide a 'default'
> numeric_limits<> with no compile-time constants, while the specializations
> do have compile-time values. Therefore, boost's numeric_limits<> is not
> picked up for these compilers; but trying to use numeric_limits<> with
user
> defined types fails to compile unless the types explicitly specialize it
> properly.
>
> I see three possible solutions here:
>
> (1) REQUIRE user defined types to *properly* specialize numeric_limits.
> (2) Enhance boost/limits.hpp so that it 'fixes' only the default
> numeric_limits<> if only that one is broken.
> (3) Define my own user specializable traits.
>
> (3) is IMO a very bad idea since we would end up with overlapping traits
and
> potential ODR violations.
> (2) might be a better solution but requires further examination.
> (1) is the easiest way to go from the library developer POV, but might
annoy
> users.

I don't actually think (2) is possible unfortunately, I would vote for (1),
it would be a precondition of your code that std::numeric_limits was
properly specialised, note however that there is at least one case (VC6 +
STLport) where numeric_limits constants are not usable in integral constant
expressions even for those templates that are specialised :-(

John Maddock
http://ourworld.compuserve.com/homepages/john_maddock/index.htm