[boost] Re: static_cast and const (Was: Re: [boost.range] lateaddition, votes needed)

From: Jonathan Turkanis (technews_at_[hidden])
Date: 2004-09-16 15:43:58

"Rob Stewart" <stewart_at_[hidden]> wrote in message:
> From: "Jonathan Turkanis" <technews_at_[hidden]>
> > "David Abrahams" <dave_at_[hidden]> wrote:
> > > "Jonathan Turkanis" <technews_at_[hidden]> writes:
> >
> > > >      template<typename Range>
> > > >      typename range_const_iterator<X>::type
> > > >      const_begin(Range& rng)
> > > >      {
> > > >          return begin(static_cast<const Range&>(rng));
> > > >      }
> > >
> > > For one thing you can't use static_cast to change constness.
> >
> > Are you sure? The expression
>
> Yep.  See 5.2.9.  You'll see what static_cast can do, and then
> 5.2.9/3 specifically excludes any other conversions.

The above cast seems to be permitted under 5.2.9/2, for the reason you snipped,
namely that

     const Range& r(rng)

is well formed.

> Modifying
> cv qualification is not among the things static_cast can do.

Then why use the language "The static_cast operator shall not cast away
constness" (5.2.9/1)?

Jonathan