On Thu, Jan 27, 2022 at 1:38 PM Manlio Perillo <manlio.peri...@gmail.com> wrote:
>
> On Thu, Jan 27, 2022 at 10:00 PM Ian Lance Taylor <i...@golang.org> wrote:
> >
> > On Thu, Jan 27, 2022 at 3:13 AM Manlio Perillo <manlio.peri...@gmail.com>
> > wrote:
> > >
> > > On Thursday, January 27, 2022 at 11:42:19 AM UTC+1 Manlio Perillo wrote:
> > [...]
> > > Here is an alternate implementation:
> > > https://gotipplay.golang.org/p/mGm8DkqkuAX
> > >
> > > The code **seems** reasonable, but the compiler reports an error:
> > > ./prog.go:24:12: *MyStruct does not implement structField
> >
> > I believe that that error message is correct. The constraint is for
> > any type whose underlying type is "*struct{ x int }". The code is
> > trying to instantiate with the type *MyStruct. The underlying type of
> > *MyStruct is *MyStruct. It is not *struct{ x int }. So the type
> > argument does not match the constraint.
> >
>
> However (from the first example) MyStruct matches struct {x int }.
> It seems a bit confusing that *MyStruct does not match *struct {x int }.
I do understand the confusion. Still, the rule for a constraint like
"~*struct{ x int }" is that the underlying type of the type argument
must be "*struct{ x int }". It's not reduce each type in the type
argument to its underlying type and see if you wind up with "*struct {
x int }"." We want to be precise here.
Ian
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