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pub trait Single {
type Item;
fn single(self) -> Option<Self::Item>;
}
impl<T, I> Single for I
where
I: IntoIterator<Item = T>,
{
type Item = T;
fn single(self) -> Option<Self::Item> {
let mut iter = self.into_iter();
// There are three cases of interest:
//
// 1. `self` has zero items -> return None.
// 2. `self` has two or more items -> return None.
// 3. `self` has exactly one item -> return `iter.next()` unchanged, as
// it holds that item.
iter.next().filter(|_| iter.next().is_none())
}
}
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