On Thursday, July 27, 2023 at 6:16:57 PM UTC-4 Michael Knyszek wrote: I believe this is working as intended, because I don't think the spec <https://go.dev/ref/spec#Conversions> makes any guarantees about the capacity of the slice you get back from a conversion.
(Other than the fact that the capacity must always be >= the length.) On Thursday, July 27, 2023 at 8:57:58 AM UTC-4 Brian Candler wrote: Interesting: https://play.golang.com/p/nSZ7tKSeot4 With the Printf commented out, it shows t has a cap of 32. With Printf uncommented, the cap drops to 0. Maybe the slice buffer is allocated on the stack in one case, and the heap on another? The slice header of 24 bytes shouldn't have anything to do with this. The cap() of a slice relates to the amount of storage allocated for the data elements (which the header points to), not the space consumed by the header itself. On Thursday, 27 July 2023 at 13:42:21 UTC+1 Brian Candler wrote: That looks very weird. The panic is triggered if I uncomment line 17 (the final fmt.Printf) even though it never reaches there - it panics when getStrBytes is called from line 9 (in line 23). On Thursday, 27 July 2023 at 13:12:40 UTC+1 Kyle Harrity wrote: I first asked this on https://reddit.com/r/golang but the contribution guide on github recommends this forum, so I'll post here before finally raising an issue on github if this appears to be a real bug. ORIGINAL POST: I came across this issue in some code I was reviewing today where a string is converted into a []byte and then a 32 byte slice is taken from that and returned. It returns a 32 byte slice even if the string is empty or less than 32 bytes in length as long as its not a string literal (comes from a function or stored in variable). I can index the slice normally and iterate over its elements, but attempting to print it with fmt.Printf causes a runtime error where it realizes the capacity is not actually 32. Trying to get a slice larger than 32 fails though smaller slices are okay. I think that has something to do with the storage needed to describe a slice 8 bytes for memory location, 8 bytes for size, 8 bytes for capacity, 8 for padding as explained here: https://stackoverflow.com/questions/67839752/why-does-an-empty-slice-have-24-bytes Here's a playground demo: https://play.golang.com/p/yiLPvRYq8PJ Maybe this is a known issue and or expected behavior so I thought I'd ask here before raising an issue on github. -- 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/8fdee71a-c30a-443b-894e-a589b43ec33en%40googlegroups.com.
