It is not clear to me under which conditions on `T` one can pass `T` around
between threads. If I run the following program
import threadpool
type Tree = object
d: int
left, right: ref Tree
template `~`[T](a: T): ref T =
var x: ref T
new(x)
x[] = a
x
proc tree(depth: int): Tree =
if depth == 0:
Tree(d: 0)
else:
Tree(d: depth, left: ~tree(depth - 1), right: ~tree(depth - 1))
proc main() =
let t = spawn tree(3)
sync()
let s = ^t
echo s
main()
I get the error `Error: cannot create a flowVar of type: Tree`. It must have to
do something with the self reference, but I am not sure why this limitation
exists
