gat_lending_iterator/adapters/
filter.rs

1use crate::LendingIterator;
2use core::fmt;
3
4/// A lending iterator that filters the elements of `iter` with `predicate`.
5///
6/// This `struct` is created by the [`filter`] method on [`LendingIterator`]. See
7/// its documentation for more.
8///
9/// [`LendingIterator`]: crate::LendingIterator
10/// [`filter`]: crate::LendingIterator::filter
11#[derive(Clone)]
12#[must_use = "iterators are lazy and do nothing unless consumed"]
13pub struct Filter<I, P> {
14    iter: I,
15    predicate: P,
16}
17
18impl<I, P> Filter<I, P> {
19    pub(crate) fn new(iter: I, predicate: P) -> Self {
20        Self { iter, predicate }
21    }
22}
23
24impl<I: fmt::Debug, P> fmt::Debug for Filter<I, P> {
25    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
26        f.debug_struct("Filter")
27            .field("iter", &self.iter)
28            .finish_non_exhaustive()
29    }
30}
31
32impl<I, P> LendingIterator for Filter<I, P>
33where
34    I: LendingIterator,
35    P: for<'a> FnMut(&I::Item<'a>) -> bool,
36{
37    type Item<'a>
38        = I::Item<'a>
39    where
40        Self: 'a;
41
42    #[inline]
43    fn next(&mut self) -> Option<Self::Item<'_>> {
44        loop {
45            // SAFETY: see https://docs.rs/polonius-the-crab/0.3.1/polonius_the_crab/#the-arcanemagic
46            let self_ = unsafe { &mut *(self as *mut Self) };
47            if let Some(item) = self_.iter.next() {
48                if (self_.predicate)(&item) {
49                    return Some(item);
50                }
51            } else {
52                return None;
53            }
54        }
55    }
56}
57
58#[cfg(test)]
59mod tests {
60    use crate::{LendingIterator, ToLendingIterator};
61
62    fn identity(x: i32) -> i32 {
63        x
64    }
65
66    #[test]
67    fn filter_basic() {
68        let result: Vec<_> = (0..10)
69            .into_lending()
70            .filter(|&x| x % 2 == 0)
71            .map(identity)
72            .into_iter()
73            .collect();
74        assert_eq!(result, vec![0, 2, 4, 6, 8]);
75    }
76}
gat_lending_iterator/adapters/filter.rs

gat_lending_iterator/adapters/
filter.rs
