When trying to use Nullable with a struct containing an
overlapping pointer:
```D
import std;
struct S
{
union
{
long foo;
int[] bar;
}
}
void main()
{
Nullable!S s;
}
```
I get this warning:
```
/dlang/dmd/linux/bin64/../../src/phobos/std/typecons.d(3820):
Deprecation: `@safe` function `toHash` calling `hashOf`
return _isNull ? 0 : .hashOf(_value.payload);
^
/dlang/dmd/linux/bin64/../../src/druntime/import/core/internal/hash.d-mixin-551(664):
and accessing overlapped field `S.bar` with pointers makes it fail to
infer `@safe`
```
The [spec](https://dlang.org/spec/function.html#safe-functions)
is states that a @safe functions "cannot access union fields that
have pointers or references overlapping with other types", and
this toHash in std.typecons is @safe.
So I wonder, why is it just a warning and not a compile error
(the code compiles and runs normally) ? Is there any risk at
ignoring this warning ?
And if there is a risk, is there a workaround or do I have to
drop the Nullable struct ?
