As to _why_ this is the case, the generics proposal has a section about that: https://go.googlesource.com/proposal/+/refs/heads/master/design/43651-type-parameters.md#permitting-constraints-as-ordinary-interface-types
On Wednesday, December 15, 2021 at 11:05:36 AM UTC-5 Jason Phillips wrote: > @Leonard, type constraints can only be used as type parameters, using them > as normal interfaces is currently not allowed. See the notes in the draft > release notes[1] or the draft 1.18 spec[2]. > > > Such interfaces may only be used as type constraints. > > > Interfaces that contain non-interface types, terms of the form ~T, or > unions may only be used as type constraints, or as elements of other > interfaces used as constraints. They cannot be the types of values or > variables, or components of other, non-interface types. > > @Kurtis, that issue is about embedded fields (fields without explicit > field names) that use type parameters. > > [1] - https://tip.golang.org/doc/go1.18 > [2] - https://tip.golang.org/ref/spec#Interface_types > > On Wednesday, December 15, 2021 at 10:47:20 AM UTC-5 kra...@skepticism.us > wrote: > >> This was asked 15 hours ago in the thread with the subject line "Go 1.18 >> beta1: Embedding Type Parameter in struct definition is an error". :-) >> >> See https://golang.org/issue/49030. >> >> On Wed, Dec 15, 2021 at 3:24 AM Leonard Mittmann <leonard....@gmail.com> >> wrote: >> >>> I just learned that type constraints, which are defined as interfaces >>> are actually not usable in all the places "normal" interfaces can be used >>> in. E.g., why can a constraint interface not be uses as a struct type? >>> >>> Let's say I have the func `func Smallest[T constraints.Ordered](s []T) T`. >>> How do I write a table test for this func? Intuitively one would try to >>> store tests like this: >>> >>> tests := []struct { >>> Arr: []constraints.Ordered >>> Want: constraints.Ordered >>> }{...} >>> >>> But this is not permitted. Am I missing something why this behavior is >>> should be considered good? If a type constraint is nothing like an >>> interface... okay, but why call it interface then? >>> >>> -- >>> 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/53df110e-8f34-490a-9b77-610dacffdbcfn%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/golang-nuts/53df110e-8f34-490a-9b77-610dacffdbcfn%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >> >> >> -- >> 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/0ae9aed8-72d4-42a2-acf0-16d0bd6b08ecn%40googlegroups.com.
