Data races make concurrency hard. They occur when two threads access the same data and at least one of them is a write. It’s trivial to write a data race, but it’s really hard to debug. Data races aren’t always clear, aren’t always reproducible, and might not always manifest in the same way. Shared mutable state is needed for a data race to occur. Value types don’t suffer from data races due to the way they work; they’re copied. When you pass an array around, copies are created. This is due to array’s value semantics. Even an object that’s a...