> It seems like since we have sharedvars, the problem solves itself: when you send an object to another thread, you don't send the sharedvar, you send the value the sharedvar is wrapping.
You never actually send sharedvars - they are not accessible at the Arc level. However, they are necessary in order to send functions across processes; the generated code expects to see sharedvars, so it has to have (a copy of) sharedvars.
> ...if a local variable is ever mutated, a 'sharedvar' C-struct is used to represent that variable. These are constructed by %sharedvar primitives, and are accessed by %sharedvar-write and %sharedvar-read primitives.