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