How to check if variable of some type can be of null value?

[JG]

On Saturday, 24 July 2021 at 20:10:37 UTC, JG wrote:
> On Saturday, 24 July 2021 at 19:39:02 UTC, Alexey wrote:
>> [...]
>
> There are probably better ways. However, this seems to work:
> ```d
> import std;
> enum canBeSetToNull(T) = __traits(compiles,(T.init is null));
>
> interface I1
> {
> }
>
> class C1 : I1
> {
> }
>
> struct S1
> {
> }
>
>     struct S2
>     {
>         int a=1;
>     }
>
>     void main()
>     {
>         auto c1 = new C1;
>
>         I1 i1 = c1;
>
>         auto s1 = S1();
>         auto s2 = S2();
>
>         static assert(canBeSetToNull!(typeof(c1)));
>         static assert(canBeSetToNull!(typeof(i1)));
>         static assert(!canBeSetToNull!(typeof(s1)));
>         static assert(!canBeSetToNull!(typeof(s2)));
>         static assert(!canBeSetToNull!(int));
>         static assert(canBeSetToNull!(int*));
>
> }```

Sorry, I see that is basically what you had.