result-iter.rs

struct ResultIter<I, F> {
	iter: I,
	f: F,
}

impl<U, E, R, F, I> Iterator for ResultIter<I, F>
where
	I: Iterator<Item = Result<U, E>>,
	F: FnOnce(U) -> Result<R, E> + Copy,
{
	type Item = Result<R, E>;
	fn next(&mut self) -> Option<Self::Item> {
		self.iter.next().map(|r| r.and_then(self.f))
	}
}

trait ResultIterator<U, E> {
	fn map_res<R, F>(self, f: F) -> ResultIter<Self, F>
	where
		F: FnOnce(U) -> Result<R, E>,
		Self: Sized;
}

impl<I, U, E> ResultIterator<U, E> for I
where
	I: Iterator<Item = Result<U, E>>,
{
	fn map_res<R, F>(self, f: F) -> ResultIter<Self, F>
	where
		F: FnOnce(U) -> Result<R, E>,
		Self: Sized,
	{
		ResultIter { iter: self, f }
	}
}