It appears to be because, deep down, the language.Tag struct contains an interface. While interfaces are "comparable", in that you can use == & !=, apparently they do not implement the 'comparable <https://pkg.go.dev/builtin#comparable>' constraint.
I'm not sure why this decision was made, though I can guess. There is probably discussion about it somewhere. It does seem to me that this should be documented the 'comparable' constraint documentation <https://pkg.go.dev/builtin#comparable>. It also makes me wonder if there are other cases where '==' compiles, but the types are not 'comparable'. On Thursday, October 6, 2022 at 7:29:46 AM UTC-4 joche...@gmail.com wrote: > Hello, > > Using "golang.org/x/text/language" I have a map of > type map[language.Tag]int. I would like to get the keys present in my > map. Why does the following command not work? > > import "golang.org/x/exp/maps" > ... > var x map[language.Tag]int > ... > fmt.Println(maps.Keys(x)) > > The error message is "Tag does not implement comparable". Code on the > playground: https://go.dev/play/p/dsyEt0ClDBH . > > The following function does work as expected, so this is easy to work > around: > > func myKeys(m map[language.Tag]int) []language.Tag { > var res []language.Tag > for key := range m { > res = append(res, key) > } > return res > } > > But I wonder now whether it is unwise to use language.Tag for the keys in > a map, and why maps.Keys() requires the keys to implement "comparable" in > addition to the constraint "M ~map[K]V". > > Many thanks, > Jochen > > > > > -- 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/7f577a92-b45c-47ca-93e1-b8684a6be0fen%40googlegroups.com.
