On Tue, Oct 3, 2023 at 12:06 PM Jon Watte <jwa...@gmail.com> wrote:
>
> I don't want to include int or struct{} in this case. I care specifically
> about "can be compared to nil"
> The only thing I can do with a type parameter that is only constrained as
> "nil" is compare it to nil, or assign nil to it.
> This means approximately "any reference type" -- interfaces, pointers, maps,
> slices, chans...
It's not obvious that that is an interesting set of types. How often
do people want to write a generic function that permits any type that
can be compared to nil but does not permit any numeric or string type?
> But, let's put this out there:
> How would you, today, write a function that compacted a slice of interface,
> such that any "nil" interface value would be removed from the slice?
Unless I misunderstand, you seem to have shifted the goal a bit.
There is currently no way to restrict a type argument to be an
interface type, with or without your suggestion of a nil constraint.
> func Compact[T ?](sl []T) []T {
> j := 0
> for i := 0; i < len(sl); i++ {
> if el := sl[i]; el != nil {
> sl[j] = el
> j++
> }
> }
> return sl[:j]
> }
>
> There's nothing today I can put in place of the "?" to make this
> perfectly-reasonable generic function work.
> I propose I should be able to put "nil" in place of the "?" to make this
> work, and it would work for any reference type (that can be compared or
> assigned to nil.)
>
> Unless I'm missing something?
Well, here is a version that works for a slice of any type, including
an interface type. Arguably, though, using reflect is cheating.
func Compact[T any](s []T) []T {
j := 0
for _, v := range s {
vv := reflect.ValueOf(v)
if vv.IsValid() && !vv.IsZero() {
s[j] = v
j++
}
}
return s[:j]
}
Ian
--
You received this message because you are subscribed to the Google Groups
"golang-nuts" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to golang-nuts+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/golang-nuts/CAOyqgcUaTdPE5-FGqqBRtr5kf-kM3b4rfsvwyFUBYu75gVZ8Ow%40mail.gmail.com.
