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

[Joseph Rushton Wakeling]

On Saturday, 14 December 2019 at 20:53:49 UTC, Dennis wrote:
>> No, that won't do.  What if you cast from a `ulong` to a 
>> `void*`?
>
> That is `@safe`, unless there is a way to corrupt memory in 
> `@safe` code by doing that.

No, it is not @safe, and for good reason.  When you cast an 
integral value to a `void*` that value gets reinterpreted as a 
memory address.  But you have absolutely no right to assume that 
it is a valid memory address.

     ulong u = 8;
     auto v = cast(void*) u;

... is totally unsafe, and the compiler rightly rejects it if you 
try to do that in a code block marked @safe.  But you shouldn't 
need the compiler to tell you to know that this is a really 
messed up thing to do.  How do you know that memory address 8 is 
in any way valid?

Things like this are WHY the spec has the rule that one cannot 
cast from a non-pointer type to `void*` in code marked @safe.