On Tue, Jan 19, 2021 at 7:06 PM burak serdar <bser...@computer.org> wrote:
>
> In the following program, it is valid to pass an interface to function P:
>
> func P[T fmt.Stringer](x T) {
> fmt.Println(x)
> }
>
> func main() {
> var v fmt.Stringer
> P(v)
> }
>
> However, there is no way for P to check if x is nil. This does not compile:
>
> func P[T fmt.Stringer](x T) {
> if x!=nil {
> fmt.Println(x)
> }
> }
>
> Is it possible to write a generic function that can test if its
> argument with a constraint is nil?
For an interface type the value "nil" is the zero value of the type,
so this is the general zero value issue mentioned at
https://go.googlesource.com/proposal/+/refs/heads/master/design/go2draft-type-parameters.md#the-zero-value
You can write
func P[T fmt.Stringer](x T) {
var zero T
if x!=zero {
fmt.Println(x)
}
}
Ian
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