Slug: conc-send-01 · Paired reading: Chapter 12
Prompt
Implement fn parallel_sum(xs: Vec<i32>) -> i32 that splits the vector in half,
sums each half on a scoped thread (or joins spawned threads with owned halves),
and returns the total. Use std::thread::scope so halves may be borrowed.
Predict first
What happens if you try thread::spawn with an Rc<Vec<i32>>?