[boost] Re: Re: Re: Re: Re: is_convertible: rationale and wording

From: Mike Conley (conley.141_at_[hidden])
Date: 2003-04-27 11:21:45

David Abrahams <dave_at_[hidden]> wrote in
news:uznmc0wpl.fsf_at_[hidden]: 

>> and_<is_const<T>, is_convertible<T,int> >.  

OK, this is wrong.  What I wanted was a boolean test: is_const<T>::value && 
is_convertible<T,int>.  That's not what and_ does.  Duh.

> It doesn't matter if it's a template parameter.  It's an ODR violation
> to have:

<snip>
 
> in the same program, which is essentially the effect if is_whatever
> uses a context-dependent is_convertible in its body.

Which is why you pass it as a boolean constant template parameter.  Then you can safely 
use that parameter in the body.  You get the context, and there's no ODR violation.
 

-- 
Mike Conley