Thank you both!
This works, see my code below. Followup question: is there a way to refer
to the new type without having to list both the element type and the
pointer type separately? Below I have to write C[A, *A], which looks
slightly ugly. And in my real application something like Creator
OrderedArray[ProperName] would look much more readable than Creator
OrderedArray[ProperName, *ProperName] .
Many thanks,
Jochen
type Type interface{}
type Settable[E Type] interface {
*E
Set(int)
}
type C[E any, P Settable[E]] struct {
Val []E
}
func (c *C[E, P]) Set(v int) {
for i := range c.Val {
var ptr P = &(c.Val[i])
ptr.Set(v)
}
}
var c = C[A, *A]{Val: []A{1, 2, 3}}
On Tuesday 23 April 2024 at 03:36:25 UTC+1 Nagaev Boris wrote:
> On Mon, Apr 22, 2024 at 9:54 PM Ian Lance Taylor <ia...@golang.org> wrote:
> >
> > On Mon, Apr 22, 2024 at 2:25 PM Jochen Voss <joche...@gmail.com> wrote:
> > >
> > > Using generics, can I somehow write a constraint which says that *T
> (instead of T) implements a certain interface? The following code
> illustrated what I'm trying to do:
> > >
> > > type A int
> > >
> > > func (a *A) Set(x int) {
> > > *a = A(x)
> > > }
> > >
> > > type B string
> > >
> > > func (b *B) Set(x int) {
> > > *b = B(strconv.Itoa(x))
> > > }
> > >
> > > type C1 struct {
> > > Val []A
> > > }
> > >
> > > func (c *C1) Set(v int) {
> > > for i := range c.Val {
> > > c.Val[i].Set(v)
> > > }
> > > }
> > >
> > > type C2 struct {
> > > Val []B
> > > }
> > >
> > > func (c *C2) Set(v int) {
> > > for i := range c.Val {
> > > c.Val[i].Set(v)
> > > }
> > > }
> > >
> > > I would like to use generics to use a single definition for the
> methods which here are func (c *C1) Set(v int) and func (c *C2) Set(v int).
> (My real code has many base types, instead of just A and B.) How can I do
> this?
> > >
> > > I tried the naive approach:
> > >
> > > type C[T interface{ Set(int) }] struct {
> > > Val []T
> > > }
> > >
> > > but when I try to use the type C[A] now, I get the error message "A
> does not satisfy interface{Set(int)} (method Set has pointer receiver)".
> >
> >
> > type C[P interface {
> > *E
> > Set(int)
> > }, E any] struct {
> > Val []P
> > }
> >
> > Ian
> >
>
> I think it should be this (s/Val []P/Val []E/):
>
> type C[P interface {
> *E
> Set(int)
> }, E any] struct {
> Val []E
> }
>
>
>
> --
> Best regards,
> Boris Nagaev
>
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