gat_lending_iterator/to_lending/
lend_refs.rs

1use crate::LendingIterator;
2
3/// A lending iterator that given an iterator, lends
4/// references to the given iterator's items.
5#[derive(Clone)]
6pub struct LendRefs<I: Iterator> {
7    item: Option<I::Item>,
8    iter: I,
9}
10
11impl<I: Iterator> LendRefs<I> {
12    pub(crate) fn new(iter: I) -> LendRefs<I> {
13        LendRefs { item: None, iter }
14    }
15}
16
17impl<I> LendingIterator for LendRefs<I>
18where
19    I: Iterator,
20{
21    type Item<'a>
22        = &'a I::Item
23    where
24        Self: 'a;
25
26    fn next(&mut self) -> Option<Self::Item<'_>> {
27        self.item = self.iter.next();
28        self.item.as_ref()
29    }
30}
31#[cfg(test)]
32mod test {
33    use crate::{LendingIterator, ToLendingIterator};
34    #[derive(Clone, Eq, PartialEq, Debug)]
35    struct Foo(usize);
36    struct W {
37        x: Foo,
38    }
39    impl LendingIterator for W {
40        type Item<'a>
41            = &'a Foo
42        where
43            Self: 'a;
44        fn next(&mut self) -> Option<Self::Item<'_>> {
45            self.x.0 += 1;
46            Some(&self.x)
47        }
48    }
49    #[test]
50    fn test() {
51        let mut xs = Vec::new();
52        test_helper().take(3).for_each(|x: &Foo| {
53            xs.push(x.clone());
54        });
55        assert_eq!(xs, vec![Foo(0), Foo(1), Foo(2)]);
56    }
57
58    fn test_helper() -> impl for<'a> LendingIterator<Item<'a> = &'a Foo> {
59        let w = W { x: Foo(0) };
60        std::iter::once(Foo(0)).lend_refs().chain(w)
61    }
62
63    #[allow(clippy::trivially_copy_pass_by_ref)]
64    fn double_ref_i32(x: &i32) -> i32 {
65        x * 2
66    }
67
68    #[test]
69    fn lend_refs_basic() {
70        let result: Vec<_> = vec![1, 2, 3]
71            .lend_refs()
72            .map(double_ref_i32)
73            .into_iter()
74            .collect();
75        assert_eq!(result, vec![2, 4, 6]);
76    }
77}
gat_lending_iterator/to_lending/lend_refs.rs

gat_lending_iterator/to_lending/
lend_refs.rs
