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

[Joseph Rushton Wakeling]

On Friday, 13 December 2019 at 08:05:53 UTC, Andrej Mitrovic 
wrote:
> However, I don't see this cast as being unsafe. Casting a class 
> object to a `void*` doesn't break the type system by itself. 
> You cannot assign a `void*` to any other pointer type without 
> an additional cast, and that additional cast would be the 
> unsafe one. Additionally, you cannot reference a `void*`, so as 
> far as I can see it's fairly safe to use in @safe code.
>
> Wouldn't it make sense to allow casting reference types to 
> `void*` in @safe code? Are there edge-cases I haven't 
> considered?

Surely where code has a cast to `void*` and then later back to 
some other pointer type, its overall safety is dependent on what 
happens at both ends.  The safety of the cast from `void*` cannot 
be validated by the developer without knowing how the cast _to_ 
`void*` was done.

Making a cast to `void*` unsafe is therefore an important push to 
the developer to say, "You need to look at this and validate what 
you're doing against how you use it later."