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pub trait FallBackOn<I> {
fn fallback(self, then: I) -> FallBack<I>;
}
pub struct FallBack<I> {
first: I,
then: I,
}
impl<I, T> FallBackOn<I> for I
where
I: Iterator<Item = T>,
{
fn fallback(self, then: I) -> FallBack<I> {
FallBack { first: self, then }
}
}
impl<I, T> Iterator for FallBack<I>
where
I: Iterator<Item = T>,
{
type Item = T;
fn next(&mut self) -> Option<T> {
self.first.next().or(self.then.next())
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn it_works() {
assert_eq!(
vec![1, 2, 3, 4, 5],
vec![1, 2, 3]
.into_iter()
.fallback(vec![0, 0, 0, 4, 5].into_iter())
.collect::<Vec<_>>()
)
}
}