Make Map a function not a method (not sure it can be made a method they way
you’re trying):
package main
import (
"fmt"
"strconv"
)
type List[T any] []T
func ToList[T any](v []T) List[T] {
return List[T](v)
}
func Map[T, U any](l List[T], f func(v T) U) List[U] {
r := make(List[U], len(l))
for i, x := range l {
r[i] = f(x)
}
return r
}
func main() {
x := []int{1, 2, 3}
y := ToList(x)
fmt.Println(y)
fmt.Printf("%q\n", Map(y, strconv.Itoa))
}
https://go2goplay.golang.org/p/F8ZojZF-ZPL
<https://go2goplay.golang.org/p/aOzuBVwfedj>
> On Feb 22, 2021, at 7:03 AM, Khosrow Afroozeh <[email protected]> wrote:
>
> I was playing with the go2go playground, and while implementing a toy List
> type, came across a few issues (Sorry if these have been discussed before, my
> cursory search didn't turn out to find anything). Given the type
>
> type List[T any] []T
>
> 1. The current go2go implementation does not allow one to do this:
>
> func ToList[T any](v []T) List[T] {
> return List(v)
> }
>
> with the error: List(v) is not a type
>
> Is this a bug, shortcoming of the current implementation, or by design? This
> would be a deal breaker if type-casting doesn't work for generics.
>
> 2. It seems impossible to implement a type-safe Map function. The following
> code:
>
> func (l List[T]) Map(f func[U any](v T) U) List[U] {
> return nil
> }
>
> will not compile, with the error: function type cannot have type parameters
> Judging by the error message this seems to be by design, but it will
> significantly reduce the usability of generics for any transformation method.
> What is the reasoning behind this limitation?
>
> Thanks,
>
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