What @xioren said: `spawn` returns a `FlowVar` and you have to wait for it to get your type.
As to your reading from `nil`, you have never constructed the `ref` which allocates it on the heap so it's still `nil` \- you can't deal with reference objects the same way as value objects just as in other languages you need to "new up" a reference. Nim threading (and also async as was suggested) are in a state of flux right now as we move to the new memory management models of Arc/Orc: the old `FlowVar`'s in the threadpool library are very restrictive as to the types with which they work as are the arguments passed to `spawn` ([see the section in the experiment part of the manual](https://nim-lang.org/docs/manual_experimental.html#parallel-amp-spawn)); a new threadpool library built to work with the new memory management doesn't exist yet and I am in process of writing it. The work around for now if you need to pass variables not compatible with `FlowVar`/`spawn` is to create pointers to the incompatible types and use those dereferenced. Messy, which is why we are moving away from it.
