how to handle shared arrays?

[maarten van damme]

Well, maybe idup is a bit better then assumeuniqe.
I don't work anymore with that mutable array on the workerthread but
using idup is in all cases allowed and cannot cause subtle bugs like
me reusing a mutable array that I've casted to immutable and send over
to another thread.
It's a shame that shared doesn't (yet) work, It looks a bit "dirty" to
convert to immutable and back to mutable simply to pass it over to
another thread...