On Tue, Aug 11, 2020 at 4:45 PM Uecker, Martin
<Martin.Uecker_at_[hidden]> wrote:
>
> Am Dienstag, den 11.08.2020, 16:41 -0400 schrieb Aaron Ballman:
> > On Tue, Aug 11, 2020 at 4:38 PM Uecker, Martin via Liaison
> > <liaison_at_[hidden]> wrote:
> > >
> > >
> > > BTW: Is
> > >
> > > if (x)
> > > int y;
> > >
> > > intentionally allowed in C++? Is there a sensible use
> > > case?
> >
> > Yes, that's well-formed C++ code. A possible use case would be for an
> > RAII object which performs work in its constructor or destructor (so
> > the declaration itself causes code to be executed).
>
> I understand this. I was thinking more about a
> high-level example where it would make sense to use
> it in this way.
>
> A file which is opened and immediately close again
> also does not make too much sense.
>
> But maybe there are better examples?

My line of thinking may be contrived, but because constructors can
accept arguments to them (including references or pointers to other
objects), the RAII object could be performing some modification. e.g.,

if (enable_special_magic)
  RAIIObject Special(Magic);

where the constructor for RAIIObject takes an argument by reference
and does something special to it (calls a function on it, modifies a
value somewhere, etc). However, I wouldn't say this is a construct
I've run across myself in the wild. As an example, perhaps the RAII
object is logging to a file in the constructor (and perhaps flushing
the file in the destructor).

~Aaron

>
> Best,
> Martin
>
>
> > ~Aaron
> >
> > >
> > > Best,
> > > Martin
> > >
> > > Am Dienstag, den 11.08.2020, 22:11 +0200 schrieb Martin Uecker:
> > > >
> > > > Am Dienstag, den 11.08.2020, 21:31 +0200 schrieb Bjarne Stroustrup:
> > > > > What benefits was this supposed to give programmers?
> > > >
> > > > It actually saves me time when writing C, because currently
> > > > have to recompile sometimes just to add a pointless
> > > > null statements. It is one of the main annoyances
> > > > when writing C.
> > > >
> > > > It is also difficult to explain to students
> > > > why you can not place a label before a declaration or
> > > > at the end of a block while it makes perfect sense
> > > > to jump there.
> > > >
> > > > C++ allows placing labels in front of declarations,
> > > > so the also improves compatibility.
> > > >
> > > > > Was the benefits worth the change to almost 50 years practice and
> > > > > documentation worth it?
> > > >
> > > > There is hardly anything to change, as it is entirely
> > > > backward compatible and simply removes an annoying
> > > > corner case from the language.
> > > >
> > > > > Are the old corner cases worse than the new ones?
> > > >
> > > > In C, there a no corner case anymore. You can place a label
> > > > everywhere you could place a statement.
> > > >
> > > >
> > > > Best,
> > > > Martin
> > > >
> > > >
> > > > > On 8/11/2020 6:43 PM, Richard Smith via Liaison wrote:
> > > > > > On Tue, 11 Aug 2020, 09:16 Uecker, Martin,
> > > > > > <Martin.Uecker_at_[hidden]
> > > > > > <mailto:Martin.Uecker_at_[hidden]>> wrote:
> > > > > >
> > > > > > Am Dienstag, den 11.08.2020, 09:04 -0700 schrieb Richard Smith:
> > > > > > > On Mon, 10 Aug 2020, 23:37 Uecker, Martin via Liaison, <
> > > > > > > liaison_at_[hidden] <mailto:liaison_at_[hidden]>> wrote:
> > > > > > >
> > > > > > > >
> > > > > > > > Hi all,
> > > > > > > >
> > > > > > > > I recently proposed changes to the C grammar which got
> > > > > > > > voted into C2X by WG14 (N2508, also see N2496).
> > > > > > > >
> > > > > > > > This allows placing of labels everywhere in a compound
> > > > > > > > statement, even before declarations and at the end
> > > > > > > > of a block, which was not possible in C so far.
> > > > > > > >
> > > > > > > > Example:
> > > > > > > >
> > > > > > > > {
> > > > > > > > start:
> > > > > > > > int i;
> > > > > > > > mid:
> > > > > > > > int j;
> > > > > > > > end:
> > > > > > > > }
> > > > > > > >
> > >
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