what exactly does cast(shared) and cast away shared do?

[Petar]

On Tuesday, 16 June 2020 at 07:22:59 UTC, mw wrote:
>
> Thanks for the explanation. I've thought &foo will return the 
> address of that actual object, just as &(foo.attr) does for 
> .attr.

To get the actual address, you need to cast the class reference 
to a pointer:

https://run.dlang.io/gist/run-dlang/ea2b163f0fd90e16adc72ab78ed48553?compiler=dmd

> So cast(shared) and cast away shared only affect the type 
> system, the actual object will always stay the same, and there 
> is not any magic operation or wrapper behind the scene.
>
> `shared` or not is purely a compile-time attribute, not some 
> runtime dynamic attribute on the object, i.e. at runtime when 
> you get hold of an object on the heap, there's no way you can 
> tell from the object itself whether it's shared or not.

Yes, exactly.