On Fri, 2010-03-05 at 15:07 -0800, Joe Buck wrote:
> On Fri, Mar 05, 2010 at 02:40:44PM -0800, Magnus Fromreide wrote:
> > On Fri, Mar 05, 2010 at 12:06:01PM -0800, Joe Buck wrote:
> > > On Fri, Mar 05, 2010 at 11:38:23AM -0800, Magnus Fromreide wrote:
> > > > Hello.
> > > >
> > > > I tried to do
> > > >
> > > > for (;; ({ break; }))
> > > > printf("Hello\n");
> > > >
> > > > and got an error message:
>
> ...
>
> > > Ideally a GNU extension should be specified as well as the rest of the
> > > standard is specified, but I'm not surprised that this doesn't work.
> >
> > So you would say this points to a buglet in the specification of statement
> > expressions?
> >
> > Or is it a bug in the C++ implementation, but one that is unimportant as it
> > is impossible to detect using standard C++?
>
> Either way, it's low priority, but if you care, I think that the "fix"
> might just be to document that certain uses don't work, and to warn the
> user that he/she isn't going to get a very good diagnostic if such uses
> are tried.
>
> If I were required to come up with a "fix", I would specify that it's not
> valid to break out of the statement expression (with a break, continue, or
> goto) and thus forbid ({ break;}), not just here but everywhere. Throwing
> exceptions would be OK because ordinary expression evaluation can throw
> exceptions.
I think that is problematic stance - at the moment the documentation
quite explicitly allows one to jump out of a statement expression.
What is needed is an added paragraph (or bullet or whatever) on some
page describing standard deviations or extensions, something like
In C++ the /for-init-statement/, /condition/ and /expression/ part of
an /iteration-statement/ are not treated as part of
the /iteration-statement/.
The effect of this is that statement expressions containing either of
break or continue in statement expressions appearing outside of
the /statement/ in a /iteration-statement/ are regarded as being outside
of the /iteration-statement/.
/MF
