I notice the gc docs say:
The following variable is provided for read-only access:
A list of objects which the collector found to be unreachable ...
This isn't clear to me. When I find finalizer cycles in gc.trash, I want to
clean them up by breaking the cycles. Unless I remove the instances from
gc.trash too, their appearance in that list keeps them alive despite that
the cycles are broken. But "read-only access" seems to imply "don't
mutate", and I don't believe that was intended. True? False?