A slice is not an array. Words to live by. > On May 26, 2021, at 7:37 PM, Kurtis Rader <kra...@skepticism.us> wrote: > > > It's more likely you've misunderstood how slices work. From > https://golang.org/ref/spec#Slice_types: > > > A slice is a descriptor for a contiguous segment of an underlying array and > > provides access to a numbered sequence of elements from that array. > > If you still believe you've found a bug we'll need the smallest reproducer > you can provide. > >> On Wed, May 26, 2021 at 5:27 PM John Olson <johnforestol...@gmail.com> 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+unsubscr...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/golang-nuts/fb9031ba-bfa0-4c92-9cb7-6ad3a8781184n%40googlegroups.com. > > > -- > Kurtis Rader > Caretaker of the exceptional canines Junior and Hank > -- > 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/CABx2%3DD-vkk_aOtNk%3D4woXcwDRy8_-pyeRu9NnRKF9beuOFSYTw%40mail.gmail.com.
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