> Is it using reference passing also for primitives like integers?
That's what I assumed, but honestly I might have misunderstood the docs. This passage is not very clear:
> Copper manipulates only references to objects. Simple data types such as integers must be seen as references to stateless objects (i.e. objects that have no state in memory).
Sounds like they store the integer in the reference itself in that case. Which also is how Ruby does things (though Ruby has to decide what is what at runtime and thus steal a couple of bits off every integer).