Zero-cost futures in Rust
I dabbled with rust in the past and was really fascinated with it, but haven't played around lately. One thing caught my eye in the post:<p><pre><code>    fn get_row(id: i32) -> impl Future<Item = Row>;
</code></pre>
That return type looks odd to me. What does it mean to return an "impl", and is that a new feature in rust, or just something advanced that I missed in my exploration before?