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

[Ola Fosheim Grøstad]

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

Sometimes you just want a set of all object identities with a 
specific property so that you can query for that property.

It is the same a the "tag"  reference type in Pony lang. It is 
safe for multi-threading too.

Say, if a thread is waiting for a set of futures to complete then 
it can remove object identities from the set based on events.