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Postings from July 2010
On 12 July 2010 13:36, demerphq <demerphq@gmail.com> wrote: > On 12 July 2010 13:07, David Golden <xdaveg@gmail.com> wrote: >> On Mon, Jul 12, 2010 at 12:51 AM, Eric Brine <ikegami@adaelis.com> wrote: >>> On Sun, Jul 11, 2010 at 10:22 PM, David Golden <xdaveg@gmail.com> wrote: >>>> >>>> I'm suggesting that we disclaim any implicit guarantee that the >>>> compiler won't optimize away expressions that have side effects when >>>> evaluated. >>> >>> Without that guarantee, >>> >>> my $x = f() >>> or DEBUG && warn(...); >>> return $x; >>> >>> would be buggy. Dunno if that matters >> >> I said "... have side effects when evaluated ..." but your example has >> a side effect (functional call) in an assignment before the logic >> expression. Maybe "evaluated" isn't the right term, but I was >> intending it to mean the action of reading a value from a variable. > > I think this is close to something i mentioned. > > My thought was: given that > > $b=$a++ + $a++; > > is not defined, that we could also assume that changing fetch magic > inside of fetch magic would only take effect after that statement > concluded, and thus > > $b=$a + $a; > > where $a is tied/overloaded and the magic changes on invocation of the > fetch is also undefined. Gah. That came out all wrong. I mean: given that $b=$a++ + $a++; is undefined, that is that an expression using a mutator on a variable mentioned twice is undefined, it seems to me that we can also consider a whole whack of fetch magic to also be undefined. > Thus we could check for magic at the beginning of the expression, and > then cache it for the duration, although we would guarantee that the > magic WAS called twice if there was magic. > > But the problem with any of these changes is that it could/would break > stuff somewhere. Which is why i figured some kind of compiler hint was > in order, as it would mean that new code could be optimised relatively > sanely and old code would continue on unbroken. > Cheers, yves -- perl -Mre=debug -e "/just|another|perl|hacker/"Thread Previous | Thread Next