1 pub trait IterExt: Iterator {
just_one(&mut self) -> Option<Self::Item>2     fn just_one(&mut self) -> Option<Self::Item> {
3         let one = self.next()?;
4         match self.next() {
5             Some(_) => None,
6             None => Some(one),
7         }
8     }
9 }
10 
11 impl<T: Iterator> IterExt for T {}
12