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
There is a little weirdness here. Maybe delcaring method on geneirc aliases
should be forbidden.
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