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pub trait TakeWhileWithFailureIterator: Iterator {
fn take_while_with_failure<P>(self, predicate: P) -> TakeWhileWithFailure<Self, P> where
P: FnMut(&Self::Item) -> bool, Self: Sized {
TakeWhileWithFailure{iter: self, flag: false, predicate: predicate}
}
}
#[derive(Clone)]
pub struct TakeWhileWithFailure<I, P> {
iter: I,
flag: bool,
predicate: P,
}
impl<I: Iterator, P> Iterator for TakeWhileWithFailure<I, P>
where P: FnMut(&I::Item) -> bool {
type Item = I::Item;
#[inline]
fn next(&mut self) -> Option<I::Item> {
if self.flag {
None
} else {
self.iter.next().and_then(|x| {
if !(self.predicate)(&x) {
self.flag = true;
}
Some(x)
})
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let (_, upper) = self.iter.size_hint();
(0, upper)
}
}
impl<'a, I: Iterator + ?Sized> TakeWhileWithFailureIterator for I {
fn take_while_with_failure<P>(self, predicate: P) -> TakeWhileWithFailure<Self, P> where Self: Sized, P: FnMut(&Self::Item) -> bool {
TakeWhileWithFailure{iter: self, flag: false, predicate: predicate}
}
}
#[test]
fn it_includes_failure() {
assert_eq!(vec![2,4,5,6].iter().take_while_with_failure(|x| (*x)%2 == 0).collect::<Vec<&i64>>(), vec![&2,&4,&5]);
}
#[test]
fn it_always_includes_the_first_element() {
assert_eq!(vec![2,4,5,6].iter().take_while_with_failure(|_| false).collect::<Vec<&i64>>(), vec![&2]);
}
#[test]
fn it_includes_all_when_true() {
assert_eq!(vec![2,4,5,6].iter().take_while_with_failure(|_| true).collect::<Vec<&i64>>(), vec![&2,&4,&5,&6]);
}
#[test]
fn it_works_on_empty_vecs() {
let empty_vec: Vec<i64> = Vec::new();
assert_eq!(empty_vec.iter().take_while_with_failure(|_| true).collect::<Vec<&i64>>().len(), 0);
}