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Re: The scope of a for statement
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.