> True, but the cost of being able to restore the original ordering, when > that restoration may not be needed at all, is prohibitive.
What about simply restoring the elements, in no particular order? This seems like an easy enough task, and I don’t think it requires the sorting algorithm to allocate any extra memory (in case no error is thrown, at least). > on Mon Jun 06 2016, Saagar Jha<saagarjha28-AT-gmail.com>wrote: > > > Might I add that leaving an array in an arbitrary and > > implementation-dependent state is also surprising to users as well as not > > very useful-to the user this is nothing more than a random permutation. > True, but the cost of being able to restore the original ordering, when > that restoration may not be needed at all, is prohibitive. It's often > the case that the caller will be throwing away the partially-modified > original when an error is thrown. > > > On Mon, Jun 6, 2016 at 5:31 PM Dave Abrahams via swift-evolution< > > swift-evolution@swift.org>wrote: > > > > > > > > on Sun Jun 05 2016, Haravikk<swift-evolution@swift.org>wrote: > > > > > > > > On 5 Jun 2016, at 19:14, Tim Vermeulen via swift-evolution< > > > swift-evolution@swift.org>wrote: > > > > > > > > > > Most standard library functions that take a closure allow that > > > > > closure to throw (and those functions are subsequently marked with > > > > > rethrows). sort and sorted are exceptions to this. I couldn’t find > > > > > > > > > this documented anywhere, but I assume this is because sorting can > > > > > happen in-place and it would be impossible to restore the array to > > > > > its original state without giving up performance. Correct me if I’m > > > > > wrong. > > > > > > > > > > I’d like to propose that we let sort rethrow anyways, and leave the > > > > > array in an intermediate state (where the elements are in an > > > > > arbitrary order) when an error is thrown. As long as this is > > > > > properly documented, this shouldn’t lead to any confusion. Best of > > > > > all, it would allow sorted to rethrow as well in which there is no > > > > > room for confusion at all because it doesn’t mutate any of the > > > > > user’s variables. > > > > > > > > This sounds reasonable; worst case with in-place sorting is that the > > > > collection was sorted in one order, and is only partially sorted in a > > > > new one, but the exception and your handling of it should be able to > > > > account for this. > > > > > > > > It will require documentation to be clear that sorting methods should > > > > take care not to leave anything incomplete if a closure throws; most > > > > algorithms should be fine since they usually just test the closure > > > > then swap two values afterwards (where necessary) so there’s nothing > > > > really to interrupt, but anything that uses some kind of buffering may > > > > need to be redesigned to ensure there’s a fallback to ensure no > > > > elements are ever lost. > > > > > > Ensuring that no elements are ever lost is not a particularly useful > > > goal, and not a constraint to which I would want to hold the standard > > > library. > > > > > > -- > > > Dave > > > > > > _______________________________________________ > > > swift-evolution mailing list > > > swift-evolution@swift.org > > > https://lists.swift.org/mailman/listinfo/swift-evolution > -- > Dave > > > _______________________________________________ swift-evolution mailing list swift-evolution@swift.org https://lists.swift.org/mailman/listinfo/swift-evolution
