From: David Abrahams (dave_at_[hidden])
Date: 2003-04-27 10:46:46
Mike Conley <conley.141_at_[hidden]> writes:
> David Abrahams <dave_at_[hidden]> wrote in
>> That completely scuttles the ODR, as far as I can tell.
> Naturally, you wouldn't want to use a built in is_convertible this way.
> Better to pass it as a template parameter directly, rather than wrapping
> it: and_<is_const<T>, is_convertible<T,int> >.
> If you know that the result of is_convertible depends on context, and you
> know about the ODR, then you know not to use is_convertible to as part of a
> metafunction's return value without also making it part of the
> metafunction's type (ie, using it as a template parameter).
It doesn't matter if it's a template parameter. It's an ODR violation
static bool const value = false;
static bool const value = true;
in the same program, which is essentially the effect if is_whatever
uses a context-dependent is_convertible in its body.
-- Dave Abrahams Boost Consulting www.boost-consulting.com
Boost list run by bdawes at acm.org, gregod at cs.rpi.edu, cpdaniel at pacbell.net, john at johnmaddock.co.uk