This is purely a type-inference problem. If you explicitly instantiate
`Append`, it works: https://goplay.tools/snippet/15RFAPFPl3y
Type inference is still relatively limited. It might become possible to at
some point omit the instantiation. I think this might be "Inferring based
on interfaces" in https://github.com/golang/go/issues/58650
Until then, it's expected that there will be some cases where you need to
specify the types.
On Sat, Oct 21, 2023 at 9:45 PM Mike Schinkel <m...@newclarity.net> wrote:
> No, that pre-generics case is not sufficient for my use-case.
>
> For my use-case I need to be able to use other types besides []Suiter such
> as []int, e.g.:
>
> var n []int
> n = Append(n, 1)
> n = Append(n, 2)
> n = Append(n, 3)
> n = Append(n, 4)
> for _, i := range n {
> fmt.Printf("Int: %d\n", i)
> }
>
> See full code in playground <https://goplay.tools/snippet/FwSn1BaWg7k>.
> On Saturday, October 21, 2023 at 3:15:03 PM UTC-4 Dan Kortschak wrote:
>
>> On Sat, 2023-10-21 at 11:58 -0700, Mike Schinkel wrote:
>> > Recently I was trying to write a func using generics where I wanted
>> > to use a slice of an interface that would contain implementers of
>> > that interface and then pass those types to a generic function, but I
>> > ran into this error:
>> >
>> > type MyStruct of MySlice{} does not match inferred type MyInterface
>> > for T
>> >
>> > My code is complex so I wrote the simplest example for this email and
>> > here is part of that code:
>> >
>> > type Suiter interface {
>> > Suit()
>> > }
>> > func Append[T any](s []T, i T) []T {
>> > return append(s, i)
>> > }
>> > func main() {
>> > var s []Suiter
>> >
>> > //CAN GENERICS SUPPORT THIS?
>> > //s = Append(s, Clubs{})
>> > //s = Append(s, Hearts{})
>> > //s = Append(s, Diamonds{})
>> > //s = Append(s, Spades{})
>> >
>> > //VERSUS HAVING TO DO THIS?
>> > s = Append(s, Suiter(Clubs{}))
>> > s = Append(s, Suiter(Hearts{}))
>> > s = Append(s, Suiter(Diamonds{}))
>> > s = Append(s, Suiter(Spades{}))
>> >
>> > for _, suit := range s {
>> > fmt.Printf("Suit: %s\n", suitName(suit))
>> > }
>> > }
>> > The full code is here in a playground.
>> >
>> > Note: My example func Append() makes no sense in real use, I only use
>> > it as it should be an easily understood example to show the syntax I
>> > am trying to illustrate.
>> >
>> > Question: Is there a way to write Append() such that I can call
>> > Append(s, Clubs{}) instead of having to write Append(s,
>> > Suiter(Clubs{}))?
>> >
>> > And if no, is there a chance that in the future Go generics will be
>> > able to support that level of type inference?
>> >
>>
>> The pre-generics language handles this case:
>> https://go.dev/play/p/jaJF7LTSVYe
>>
>> Is there something about your real case that makes this not acceptable?
>>
>> --
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