Casting Pointers?

[Stefan Koch via Digitalmars-d]

On Thursday, 12 May 2016 at 08:41:25 UTC, John Burton wrote:
> I've been unable to find a clear definitive answer to this so 
> please point me to one if it already exists in the manual or 
> the forums.
>
> Is it safe to cast pointer types?
>
>     double data;
>     long p = *cast(long*)&data;
>
> (Excuse any silly syntax errors as I'm doing this on my phone).
>
> This used to be possible in C until people recently decided it 
> not only was wrong, it had always been wrong :P (Ok I'm not 
> entirely serious there but that's what this issue feels like...)
>
> Is this legal / valid in D and if not what is the appropriate 
> way to efficiently access data like this?

How would such a cast be safe?