On Wed, Jun 17, 2020 at 3:52 PM jimmy frasche <soapboxcic...@gmail.com> wrote:
>
> The only case I mean is when the intersection of the type lists is ∅.
> That's easy to check and always wrong afaict.
Unfortunately I don't think it's that simple.
type MyInt int
type I1 interface {
type int
}
type I2 interface {
type MyInt
}
type I3 interface {
I1
I2
}
It might seem like the intersection of the type lists in I1 and I2 is
the empty set, but since we match on underlying types I3 does match
"int".
Ian
> On Wed, Jun 17, 2020 at 3:47 PM Ian Lance Taylor <i...@golang.org> wrote:
> >
> > On Wed, Jun 17, 2020 at 1:09 PM jimmy frasche <soapboxcic...@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
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