An empty intersection of type lists cannot be instantiated with any actual type, but if type-list interfaces could eventually be used as run-time types (as suggested in https://golang.org/design/go2draft-type-parameters#type-lists-in-interface-types), then the interface with an empty type-list would be meaningful: it would be an interface type whose only valid value is nil.
(In more formal terms, it would be the unique bottom element of the interface-type lattice, equivalent to the nil case in a type-switch today.) On Wednesday, June 17, 2020 at 6:54:00 PM UTC-4 soapboxcicero wrote: > The only case I mean is when the intersection of the type lists is ∅. > That's easy to check and always wrong afaict. > > On Wed, Jun 17, 2020 at 3:47 PM Ian Lance Taylor <ia...@golang.org> > wrote: > > > > On Wed, Jun 17, 2020 at 1:09 PM jimmy frasche <soapbo...@gmail.com> > wrote: > > > > > > This isn't a bug per se, but I can file one if requested. > > > > > > https://go2goplay.golang.org/p/AWynhg6ya7h > > > > > > Since embedding interfaces with type lists uses the intersection of > > > the items in the type list, it's possible to create an interface that > > > cannot be satisfied by any type. > > > > > > Currently this does not cause an error until you attempt to > > > instantiate something that uses such an interface as a bound. > > > > > > I think it would be more useful to raise the error when defining the > > > interface that cannot be used as it's likely an error—or at least I > > > can see no valid use for creating an unsatisfiable constraint. > > > > In order to ensure that all Go compilers act the same, we would have > > to very carefully define the cases that are not accepted. This is a > > little harder than it sounds since matching is done on underlying > > types. At least for now I tend to think that it would be better to > > make this a vet check. But I don't feel all that strongly about it. > > > > Ian > -- 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/11a2ccef-f8e5-4de6-9374-c2f72e309b4fn%40googlegroups.com.
