Thank you! I've now switched to using any as you suggested & also use strings.Builder.
On Wednesday, November 9, 2022 at 4:33:48 PM UTC dun...@harris3.org wrote: > > Interestingly, I couldn't put the asStr() code in the String() function > since doing so produced this error: > > > > invalid operation: cannot use type assertion on type parameter value > element (variable of type T constrained by comparable) > > You need to convert to "any": https://go.dev/play/p/1pMhs22S-8P > > P.S. It would be better to use https://pkg.go.dev/strings#Builder for > building a string > > On Tuesday, 8 November 2022 at 13:09:51 UTC Mark wrote: > >> Thanks for your help and very interesting ideas. In the end I used this: >> >> type Set[T comparable] map[T]struct{} >> >> func New[T comparable](elements ...T) Set[T] { >> set := make(Set[T], len(elements)) >> for _, element := range elements { >> set[element] = struct{}{} >> } >> return set >> } >> >> func (me Set[T]) String() string { >> elements := make([]T, 0, len(me)) >> for element := range me { >> elements = append(elements, element) >> } >> sort.Slice(elements, func(i, j int) bool { >> return less(elements[i], elements[j]) >> }) >> s := "{" >> sep := "" >> for _, element := range elements { >> s += sep + asStr(element) >> >> sep = " " >> } >> return s + "}" >> } >> >> func asStr(x any) string { >> if s, ok := x.(string); ok { >> return fmt.Sprintf("%q", s) >> } >> return fmt.Sprintf("%v", x) >> } >> >> func less(a, b any) bool { >> switch x := a.(type) { >> case int: >> return x < b.(int) >> case float64: >> return x < b.(float64) >> case string: >> return x < b.(string) >> default: >> return fmt.Sprintf("%v", a) < fmt.Sprintf("%v", b) >> } >> } >> >> Interestingly, I couldn't put the asStr() code in the String() function >> since doing so produced this error: >> >> invalid operation: cannot use type assertion on type parameter value >> element (variable of type T constrained by comparable) >> >> Anyway, I'm happy that it all works now. (I know I ought to include every >> int & float32, but this is enough for now). >> >> >> >> On Tuesday, November 8, 2022 at 11:29:34 AM UTC rog wrote: >> >>> If you're sure that T is an int or a string, then why not constrain it >>> as such? https://go.dev/play/p/1kT6EacMHco >>> >>> You could go further and constrain it to allow any type with ordering >>> defined: https://go.dev/play/p/il5koj1RPkh >>> >>> If you want to allow any kind of comparable key in your set, one could >>> observe that essentially you're trying to solve the same problem that the >>> fmt package is solving when it converts maps to string. It uses the >>> internal fmtsort <https://pkg.go.dev/internal/fmtsort> package, which, >>> as luck would have it, has been factored out into an externally >>> available package >>> <https://pkg.go.dev/github.com/rogpeppe/go-internal/fmtsort>. So you >>> could do this: https://go.dev/play/p/oKTGSm_o22a >>> >>> To answer the specific question you asked, there is an issue that tracks >>> the ability to do a switch directly on a type parameter: >>> https://github.com/golang/go/issues/45380 >>> >>> But you can also work around the lack of that feature by doing something >>> like this: https://go.dev/play/p/3C2a61Ojbxs >>> >>> Hope this helps, >>> >>> rog. >>> >>> >>> On Tue, 8 Nov 2022 at 08:53, 'Mark' via golang-nuts < >>> golan...@googlegroups.com> wrote: >>> >>>> Given a function: >>>> >>>> func F[T comparable](a T) { >>>> } >>>> >>>> is it possible to check T's type inside F? >>>> >>>> My use case is that I have a function with signature G[T comparable](x >>>> []T) and inside G I want to sort the elements in slice x where T could be >>>> int or string. >>>> >>>> This arises in a tiny generic set module I've created: >>>> https://github.com/mark-summerfield/gset >>>> In the String() method I want to return a string with the elements >>>> sorted (for human readability and for testing convenience); but at the >>>> moment I can only do this by converting all elements to strings and >>>> sorting >>>> them which isn't good for ints. >>>> >>>> -- >>>> 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. >>>> To view this discussion on the web visit >>>> https://groups.google.com/d/msgid/golang-nuts/e746f065-24fa-474a-90ec-2d8367bf3e3bn%40googlegroups.com >>>> >>>> <https://groups.google.com/d/msgid/golang-nuts/e746f065-24fa-474a-90ec-2d8367bf3e3bn%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/fc707f5e-0f80-4224-9532-b97ad3a9eea5n%40googlegroups.com.
