Re: Type traits direct compiler support

From: Edward Diener (eddielee_at_[hidden])
Date: 2002-10-15 08:48:34

> > From: Edward Diener [mailto:eddielee_at_[hidden]]
> >
> > What does it mean in the type_traits documentation that "direct compiler
> > support for that traits class is required" ? I do not see that
terminology
> > explained anywhere and am lost as far as to what it refers.
>
> It means that there is no known way to implement that class (in a
> Standard-compliant, portable manner).
>
> The type traits library is in a rather uncomfortable position, since it is
> essentially trying to add reflection to the C++ language after the fact.
>
> As currently implemented, the type traits library bends over backwards to
> try to provide as much as possible to as many different compilers as
> possible.  But the simple fact is that it should not really be a library,
> but a part of the supplied language.
>
> Some type traits classes technically require compiler support.  However,
> those classes will all try to take their "best guess" at the correct
answer
> -- sometimes defaulting to a "safe" default if they can't figure out the
> correct answer.

What sort of compiler support is being talked of here, since  you mention
that it can't be done in a standard-compliant manner ? Does this mean
looking at preprocessor defines to determine the correct results, or what ?
It is the vagueness of the term "compiler support", which you did not
alleviate in your answer, which I am trying to clarify.