Since I picked Rust ahead of time, the coding round was centered on that. They gave me a trait and asked me to implement it. You also have to write your own tests and walk through how it works, plus explain what the expected outcomes are. There's not really a 'right' answer here - it's about tradeoffs. You need to be specific and reason through your choice. For example, you could go with a zero-allocated buffer on the stack, or you could use an empty buffer on the heap. I knew how to approach this one because I've worked a lot with `BufWriter` in `std::io`. It helped me talk through how it deals with panics and partial writes, which turned out to be really relevant.