Shouldn't casting an object to void* be considered @safe?

[Dennis]

On Saturday, 14 December 2019 at 17:54:20 UTC, Joseph Rushton 
Wakeling wrote:
> What's the point in generating a pure object identity, or a set 
> of objects, unless those objects are going to be used?

Whether something is useful or a good practice is not relevant 
for @safe, it is only concerned with whether it makes memory 
corruption possible.

> And how do you validate that that usage is safe without knowing
> something about the circumstances in which those pure 
> identities were generated?

Any function that takes a void* and casts it to a different 
pointer that gets dereferenced is not @safe, whether class 
casting to void* is allowed or not. You simply can't assume 
anything about a void* even in @safe code.
Note that casting pointer types to void is already allowed in 
@safe:

```
class C {}
void main() @safe {
     void* v0 = cast(void*) new int; // allowed, implicit 
conversion
     void* v1 = cast(void*) 0xDEAFBEEF; // not allowed, not a 
pointer type
     void* v2 = cast(void*) new C(); // not allowed, not a pointer 
type
}
```

The spec says:

> - No casting from a pointer type to any type other than void*.
> - No casting from any non-pointer type to a pointer type.

https://dlang.org/spec/function.html#safe-functions

The second line could be changed to "No casting from any 
non-pointer type to a pointer type other than void*" however.