Thanks for the reply.
Does that mean it's currently not possible to conditionally implement a
method based on type parameters? And the solution should probably be that I
use CanConvert from reflect do that at runtime?
On Monday, November 4, 2024 at 1:47:30 PM UTC+8 Ian Lance Taylor wrote:
> On Sun, Nov 3, 2024 at 12:41 AM hey...@gmail.com <hey...@gmail.com> wrote:
> >
> > Not sure generic type alias is the solution, but what I'm trying to do
> is I have a type like this
> >
> > type Map[K comparable, V any] struct { m map[K]V }
> >
> > and I want it to implement json.Unmarshaller to decode json objects,
> when K's underlying type is string:
> >
> > type omap[K ~string, V any] = Map[K, V]
> > func (m *omap[K, V]) UnmarshalJSON(data []byte) error {
> > k := "a"
> > v :=1
> > m[K(k)] = v
> > }
> >
> > Go 1.23 with the aliastypeparams flag enabled, currently complains
> "cannot convert k (variable of type string) to type K".
> >
> > I wonder if using alias this way is wrong and if there exists another
> solution?
>
> A type alias is just an alias. When you declare a method on the alias
> map, you are declaring a method on the type Map. That means that the
> ~string in the omap definition is ignored for the method definition;
> all that matters is the comparable constraint in the Map definition.
> You can't in general convert a string to a comparable type.
>
> Ian
>
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