> It seems to me `== nil` is a better way to spell that, than a function
call. And a generic function can always do `v == *new(T)` to check if a
value is the zero value.
Bringing this up because I found it from a thread on Google.
I want to implement a generic function to "remove nil values from a slice."
This should be able to remove nil instances of error, for example.
So, let's say I have:
var arg = []error{nil, errors.New("oh noes"), nil}
Unfortunately, this doesn't work:
func Compact[T comparable](s []T) T {
...
if s[i] == nil {
because "error" is not comparable.
This also doesn't work:
func Compact[T any](s []T) T {
var zero T
...
if s[i] == zero {
because T is not a comparable constraint.
It may be that "error" is somehow special, and is "the only thing" that
doesn't fit neatly into "zero values" or "comparables," but it's a pretty
basic fundament of the runtime, so having to special-case everything about
it is quite frustrating and cumbersome.
Sincerely
Jon Watte
On Thursday, December 22, 2022 at 5:39:29 AM UTC-8 Axel Wagner wrote:
> On Thu, Dec 22, 2022 at 2:23 PM Pierre Durand <pierre...@gmail.com> wrote:
>
>> Is there a way to declare a "nillable" constraint that matches all types
>> that can be nil (pointer, slice, map, etc.) ?
>
>
> There is currently no way to do that. In particular, any interface type
> can be `nil`, therefore any such constraint would have to be satisfied by
> all interface types.
>
>
>> I would like to write a function, that receives a parameter (with a
>> generic type), and check if this parameter is nil.
>>
>
> I don't understand the point, to be honest. It seems to me `== nil` is a
> better way to spell that, than a function call. And a generic function can
> always do `v == *new(T)` to check if a value is the zero value.
>
>
>> I found a very ugly way to write it: https://go.dev/play/p/0g0SoTlBEgs
>> The problem: the map type needs more than 1 type, so I need to provide
>> the 3 types when I call the `IsNil()` function/
>> Is there a better way ?
>>
>> Yes I know I could use `any`, and check with reflect if the value inside
>> the interface is nil.
>> But I want to know if it's possible to do it with generics.
>>
>> Thank you.
>>
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