On Tue, 2021-01-19 at 19:38 -0800, Ian Lance Taylor wrote:
> 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
Would that work for non-comparable types? Say the T has an underlying
[]int type, then the comparison is not against nil and you end up with
a panic.
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