2 #![feature(trait_upcasting)]
8 impl<X: A + B> C for X {}
10 pub fn test<'a, T>(view: T) -> Option<&'a mut dyn B>
12 T: IntoIterator<Item = &'a mut dyn B>,
14 return Some(view.into_iter().next().unwrap());
18 let mut a: Vec<Box<dyn C>> = Vec::new();
19 test(a.iter_mut().map(|c| c.as_mut() as &mut dyn B));