Thank you! So it seems I misunderstood what append() does. I expected that all of the slices I had created with append() would have just enough capacity, such that every use of append() would allocate new memory and copy. It surprises me that my code worked as well as it did.
J > On May 26, 2021, at 21:51, Jamil Djadala <djad...@gmail.com> wrote: > > minimally changed code that works: > > https://play.golang.org/p/Tcfw_EC8jMp > > > On Thursday, May 27, 2021 at 4:11:40 AM UTC+3 johnfor...@gmail.com wrote: > Here’s the code. <https://play.golang.org/p/JYXqCWsXeIj> It might be possible > to come up with a shorter reproducer, but I’m not sure where to start. The > recursion takes place in line 21. The code works for 7 or smaller, and fails > for 8 and larger. > > J > > >> On May 26, 2021, at 20:34, Martin Schnabel <m...@mb0.org >> <applewebdata://FFD37931-C171-49EF-A02A-79DF957E69FF>> wrote: >> >> Could you send a https://play.golang.org/ <https://play.golang.org/> link >> showing a short example? >> >> Without much information it sounds like a you update the same slice at two >> different indices. It would be interesting to know how you populate the temp >> slice. >> >> On 27.05.21 01:52, John Olson wrote: >>> I have a recursive function that seems to be reusing memory it shouldn't. >>> I'm developing in Goland 2021.1.1 with go version 1.16.2. >>> I've written a function to generate the partitions of an integer. The >>> partitions of n are all the sets of integers that add up to n, so the >>> partitions of 3 are {3}, {2,1} and {1,1,1}. As n grows, the number of >>> partitions grows exponentially (to be precise, as e^(n^½)). I wrote a >>> recursive function, which works great up to n=7. At n=8, one of the >>> partitions is {2,2,2,1}, which is obviously wrong; and since the function >>> is recursive, every subsequent n is wrong, too. >>> I just spent quite a long time stepping through the code, and I found that >>> what seems to be happening is that a slice declared in my recursive >>> function is being reused in two different recursions. Specifically, my >>> function declares >>> var temp [][]int >>> to build up the list of partitions. When I compute Partitions(8), I have to >>> compute Partitions(4), 5, 6 and 7. I memoize each set of partitions so I >>> only have to compute them once. >>> It all goes wrong when I'm working on Partitions(7). At this point, >>> Partitions(8) has already added 6 cases, the last of which is {2,2,2,2}. >>> This is stored in temp[5], the temp corresponding to n=8, of course. Then I >>> compute Partitions(7), which should create a new temp [][]int; I'll call >>> this temp//7. temp[6]//7 gets {2,2,2,1}, and at that point temp[5]//8 >>> changes from {2,2,2,2} to {2,2,2,1}. The addresses of temp[6]//7 and >>> temp[5]//8 are different, but the addresses of the /elements/ of these >>> slices are the same. >>> This has to be wrong. >>> I suspect a bug in go, but I suppose it's possible there's a bug in goland. >>> I'm running on macOS 11.3.1, just in case that's relevant. >>> I'm happy to share the source code if anyone is interested. >>> Thanks, >>> J >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "golang-nuts" group. >>> To unsubscribe from this group and stop receiving emails from it, send an >>> email to golang-nuts...@googlegroups.com >>> <applewebdata://FFD37931-C171-49EF-A02A-79DF957E69FF> >>> <mailto:golang-nuts...@googlegroups.com >>> <applewebdata://FFD37931-C171-49EF-A02A-79DF957E69FF>>. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/golang-nuts/fb9031ba-bfa0-4c92-9cb7-6ad3a8781184n%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/golang-nuts/fb9031ba-bfa0-4c92-9cb7-6ad3a8781184n%40googlegroups.com> >>> >>> <https://groups.google.com/d/msgid/golang-nuts/fb9031ba-bfa0-4c92-9cb7-6ad3a8781184n%40googlegroups.com?utm_medium=email&utm_source=footer >>> >>> <https://groups.google.com/d/msgid/golang-nuts/fb9031ba-bfa0-4c92-9cb7-6ad3a8781184n%40googlegroups.com?utm_medium=email&utm_source=footer>>. > > > -- > You received this message because you are subscribed to a topic in the Google > Groups "golang-nuts" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/golang-nuts/MPQWVYruhlU/unsubscribe > <https://groups.google.com/d/topic/golang-nuts/MPQWVYruhlU/unsubscribe>. > To unsubscribe from this group and all its topics, send an email to > golang-nuts+unsubscr...@googlegroups.com > <mailto:golang-nuts+unsubscr...@googlegroups.com>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/de91d8a7-63eb-40aa-bf20-b1a18897fa84n%40googlegroups.com > > <https://groups.google.com/d/msgid/golang-nuts/de91d8a7-63eb-40aa-bf20-b1a18897fa84n%40googlegroups.com?utm_medium=email&utm_source=footer>. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/7FC72E06-30BA-4AF0-BA4C-8A1A7162FBF1%40gmail.com.
