1 use itertools::Itertools;
2
3 struct PanickingCounter {
4 curr: usize,
5 max: usize,
6 }
7
8 impl Iterator for PanickingCounter {
9 type Item = ();
10
next(&mut self) -> Option<Self::Item>11 fn next(&mut self) -> Option<Self::Item> {
12 self.curr += 1;
13
14 assert_ne!(
15 self.curr, self.max,
16 "Input iterator reached maximum of {} suggesting collection by adaptor",
17 self.max
18 );
19
20 Some(())
21 }
22 }
23
no_collect_test<A, T>(to_adaptor: T) where A: Iterator, T: Fn(PanickingCounter) -> A,24 fn no_collect_test<A, T>(to_adaptor: T)
25 where
26 A: Iterator,
27 T: Fn(PanickingCounter) -> A,
28 {
29 let counter = PanickingCounter {
30 curr: 0,
31 max: 10_000,
32 };
33 let adaptor = to_adaptor(counter);
34
35 for _ in adaptor.take(5) {}
36 }
37
38 #[test]
permutations_no_collect()39 fn permutations_no_collect() {
40 no_collect_test(|iter| iter.permutations(5))
41 }
42
43 #[test]
combinations_no_collect()44 fn combinations_no_collect() {
45 no_collect_test(|iter| iter.combinations(5))
46 }
47
48 #[test]
combinations_with_replacement_no_collect()49 fn combinations_with_replacement_no_collect() {
50 no_collect_test(|iter| iter.combinations_with_replacement(5))
51 }
52