OK, I will try it several days later. On Saturday, November 13, 2021 at 1:21:08 AM UTC+8 axel.wa...@googlemail.com wrote:
> Yes, the doc is outdated. Since then, several changes have been made to > the design, to accomodate issues that either came up during the discussion > or where discovered after - one of the more significant is > https://github.com/golang/go/issues/45346, but there are others. > That's why I said we should probably wait for the actual spec changes > before discussing it further, as there currently is no single authoritative > source for what will land in go 1.18. > > On Fri, Nov 12, 2021 at 6:18 PM tapi...@gmail.com <tapi...@gmail.com> > wrote: > >> The SliceConstraint example also doesn't work. >> >> Is the doc I mentioned outdated? >> >> On Saturday, November 13, 2021 at 1:13:13 AM UTC+8 tapi...@gmail.com >> wrote: >> >>> And this fails to compile, although the docs says it is valid: >>> >>> // sliceOrMap is a type constraint for a slice or a map. >>> type sliceOrMap interface { >>> []int | map[int]int >>> } >>> >>> // Entry returns the i'th entry in a slice or the value of a map >>> // at key i. This is valid as the result of the operator is always >>> int. >>> func Entry[T sliceOrMap](c T, i int) int { >>> // This is either a slice index operation or a map key lookup. >>> // Either way, the index and result types are type int. >>> return c[i] // invalid operation: cannot index c (variable of >>> type T constrained by sliceOrMap >>> } >>> >>> >>> On Saturday, November 13, 2021 at 1:10:30 AM UTC+8 tapi...@gmail.com >>> wrote: >>> >>>> The proposal design docs ( >>>> https://go.googlesource.com/proposal/+/refs/heads/master/design/43651-type-parameters.md) >>>> >>>> mentions: >>>> >>>> // structField is a type constraint whose type set consists of some >>>> // struct types that all have a field named x. >>>> type structField interface { >>>> struct { a int; x int } | >>>> struct { b int; x float64 } | >>>> struct { c int; x uint64 } >>>> } >>>> >>>> // This function is INVALID. >>>> func IncrementX[T structField](p *T) { >>>> v := p.x // INVALID: type of p.x is not the same for all types >>>> in set >>>> v++ >>>> p.x = v >>>> } >>>> >>>> However, it still fails to compile if all the types of the x fields are >>>> identical. >>>> >>>> type structField interface { >>>> struct { a int; x int } | >>>> struct { b int; x int } | >>>> struct { c int; x int } >>>> } >>>> >>>> func IncrementX[T structField](p *T) { >>>> v := p.x // p.x undefined (type *T has no field or method x) >>>> v++ >>>> p.x = v // p.x undefined (type *T has no field or method x) >>>> } >>>> >>>> >>>> >>>> -- >> 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/785df174-2e12-49bc-a3af-f143a89cd831n%40googlegroups.com >> >> <https://groups.google.com/d/msgid/golang-nuts/785df174-2e12-49bc-a3af-f143a89cd831n%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/56b07f60-9928-4e21-b2f7-5358c05a9306n%40googlegroups.com.
