Yes, it's sort of like asking what the best way to translate "This
sentence is not Spanish." into Spanish; you can do it, but it doesn't
make a lot of sense.
On Wed, 2020-09-16 at 02:13 -0700, Volker Dobler wrote:
> On Wednesday, 16 September 2020 at 10:51:27 UTC+2
> stephan...@gmail.com wrote:
> > Assume a public interface I with two methods NotInS and M whereas
> > NotInS
> > is calling M. An implementation i of I which implements NotInS and
> > M as
> > well as a specialization s of i which only implements M. Finally a
> > constructor whose return-type is I returns a pointer to an instance
> > of
> > s. Calling on this return-value NotInS will execute i.M() as the
> > following test shows. I would like it to call s.M(). How would I
> > do
> > this in a goish way? Thanks for any help!
>
> Well, start of by not using Java/C#/C++ terminology as Go is
> different
> and in Go you simply cannot have a "specialization s of i" as there
> are
> no "specialization" as there is no inheritance. Also let's rewrite
> the code
> to be a bit more Go'ish:
>
> package main
>
> import "fmt"
>
> type I interface {
> NotInS()
> M()
> }
>
> type T struct{}
> func (t *T) NotInS() { t.M() }
> func (t *T) M() { fmt.Println("T.M") }
>
> type S struct{ *T }
> func (s *S) M() { fmt.Println("S.M") }
>
> func main() {
> x := &S{&T{}}
> x.NotInS()
> }
>
> You see S has no method NotInS defined and all calls to
> NotInS are automatically directed to implicit field T of
> S. Remember that embedding a *T in an S has nothing to
> do with inheritance or specialisation. It is just some tiny
> syntactic sugar for an implicit field and automatic method
> forwarding to that field. Spelling it out your code is
> equivalent to:
> type S struct{ T *T }
> func (s *S) NotInS() { s.T.M() }
>
> The embedded T doesn't know it is a field of S and you
> call T's M method and it is simply impossible to have
> S's M method called like this.
>
> You must redesign. Embedding is not inheritance and
> you cannot modle inheritance based design with embedding
> no matter how hard you try.
>
> V.
>
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