On Fri, 5 Jan 2024 at 05:58, 'Axel Wagner' via golang-nuts <
golang-nuts@googlegroups.com> wrote:
> Hi,
>
> I think the reason this has not happened is that it makes code using such
> a type invalid, depending on the type-argument - in ways not captured by
> the constraint. For example:
>
> type X[T any] struct {
> T
> *bufio.Reader
> }
> func main() {
> var x X[int]
> x.Read // definitely refers to X.Reader.Read
> var y X[*strings.Reader]
> y.Read // ambiguous
> }
>
> Note, in particular, that this might happen very deeply in the call stack,
> as you can have a generic function instantiating a generic type with a type
> parameter as well.
>
> func main() {
> F[*strings.Reader]()
> }
> func F[T any]() {
> G[T]()
> }
> func G[T any]() {
> var x X[T]
> x.Read
> }
>
> For us to actually allow embedding that way, one of three things would
> need to happen:
>
To my mind, there's a reasonably obvious way through the issue you outlined
above (although there may well be more):
allow a static reference to a field/method if all the embedded types are
known, and not otherwise.
So in the above example, `x.Read` in `main` is fine; `y.Read` in `main` is
ambiguous due to two methods at the same level as you say;
`x.Read` in `G` is not allowed because we don't statically know the method
set of `x`. Likewise, we couldn't assign `x` to an `io.Reader`,
but we *could* convert to `any` and then do a dynamic type conversion to
`io.Reader` if we wished (which would fail in the *strings.Reader case
but succeed in the int case).
ISTM those semantics would be reasonably intuitive, and good compiler error
messages could make it quite clear *why* we aren't allowed to reference
such methods statically.
cheers,
rog.
>
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