6 fn test_iterator_flatten() {
8 let ys = [0, 1, 2, 3, 4, 5, 6, 7, 8];
9 let it = xs.iter().map(|&x| (x..).step_by(1).take(3)).flatten();
15 assert_eq!(i, ys.len());
18 /// Tests `Flatten::fold` with items already picked off the front and back,
19 /// to make sure all parts of the `Flatten` are folded correctly.
21 fn test_iterator_flatten_fold() {
23 let ys = [1, 2, 3, 4, 5, 6, 7];
24 let mut it = xs.iter().map(|&x| x..x + 3).flatten();
25 assert_eq!(it.next(), Some(0));
26 assert_eq!(it.next_back(), Some(8));
27 let i = it.fold(0, |i, x| {
31 assert_eq!(i, ys.len());
33 let mut it = xs.iter().map(|&x| x..x + 3).flatten();
34 assert_eq!(it.next(), Some(0));
35 assert_eq!(it.next_back(), Some(8));
36 let i = it.rfold(ys.len(), |i, x| {
37 assert_eq!(x, ys[i - 1]);
44 fn test_flatten_try_folds() {
45 let f = &|acc, x| i32::checked_add(acc * 2 / 3, x);
46 let mr = &|x| (5 * x)..(5 * x + 5);
47 assert_eq!((0..10).map(mr).flatten().try_fold(7, f), (0..50).try_fold(7, f));
48 assert_eq!((0..10).map(mr).flatten().try_rfold(7, f), (0..50).try_rfold(7, f));
49 let mut iter = (0..10).map(mr).flatten();
51 iter.next_back(); // have front and back iters in progress
52 assert_eq!(iter.try_rfold(7, f), (1..49).try_rfold(7, f));
54 let mut iter = (0..10).map(|x| (4 * x)..(4 * x + 4)).flatten();
55 assert_eq!(iter.try_fold(0, i8::checked_add), None);
56 assert_eq!(iter.next(), Some(17));
57 assert_eq!(iter.try_rfold(0, i8::checked_add), None);
58 assert_eq!(iter.next_back(), Some(35));
62 fn test_flatten_non_fused_outer() {
63 let mut iter = NonFused::new(once(0..2)).flatten();
65 assert_eq!(iter.next_back(), Some(1));
66 assert_eq!(iter.next(), Some(0));
67 assert_eq!(iter.next(), None);
68 assert_eq!(iter.next(), None);
70 let mut iter = NonFused::new(once(0..2)).flatten();
72 assert_eq!(iter.next(), Some(0));
73 assert_eq!(iter.next_back(), Some(1));
74 assert_eq!(iter.next_back(), None);
75 assert_eq!(iter.next_back(), None);
79 fn test_flatten_non_fused_inner() {
80 let mut iter = once(0..1).chain(once(1..3)).flat_map(NonFused::new);
82 assert_eq!(iter.next_back(), Some(2));
83 assert_eq!(iter.next(), Some(0));
84 assert_eq!(iter.next(), Some(1));
85 assert_eq!(iter.next(), None);
86 assert_eq!(iter.next(), None);
88 let mut iter = once(0..1).chain(once(1..3)).flat_map(NonFused::new);
90 assert_eq!(iter.next(), Some(0));
91 assert_eq!(iter.next_back(), Some(2));
92 assert_eq!(iter.next_back(), Some(1));
93 assert_eq!(iter.next_back(), None);
94 assert_eq!(iter.next_back(), None);
98 fn test_double_ended_flatten() {
100 let v = [5, 6, 7, 8];
101 let mut it = u.iter().map(|x| &v[*x..v.len()]).flatten();
102 assert_eq!(it.next_back().unwrap(), &8);
103 assert_eq!(it.next().unwrap(), &5);
104 assert_eq!(it.next_back().unwrap(), &7);
105 assert_eq!(it.next_back().unwrap(), &6);
106 assert_eq!(it.next_back().unwrap(), &8);
107 assert_eq!(it.next().unwrap(), &6);
108 assert_eq!(it.next_back().unwrap(), &7);
109 assert_eq!(it.next_back(), None);
110 assert_eq!(it.next(), None);
111 assert_eq!(it.next_back(), None);
115 fn test_trusted_len_flatten() {
116 fn assert_trusted_len<T: TrustedLen>(_: &T) {}
117 let mut iter = array::IntoIter::new([[0; 3]; 4]).flatten();
118 assert_trusted_len(&iter);
120 assert_eq!(iter.size_hint(), (12, Some(12)));
122 assert_eq!(iter.size_hint(), (11, Some(11)));
124 assert_eq!(iter.size_hint(), (10, Some(10)));
126 let iter = array::IntoIter::new([[(); usize::MAX]; 1]).flatten();
127 assert_eq!(iter.size_hint(), (usize::MAX, Some(usize::MAX)));
129 let iter = array::IntoIter::new([[(); usize::MAX]; 2]).flatten();
130 assert_eq!(iter.size_hint(), (usize::MAX, None));
132 let mut a = [(); 10];
133 let mut b = [(); 10];
135 let iter = array::IntoIter::new([&mut a, &mut b]).flatten();
136 assert_trusted_len(&iter);
137 assert_eq!(iter.size_hint(), (20, Some(20)));
138 core::mem::drop(iter);
140 let iter = array::IntoIter::new([&a, &b]).flatten();
141 assert_trusted_len(&iter);
142 assert_eq!(iter.size_hint(), (20, Some(20)));
144 let iter = [(), (), ()].iter().flat_map(|_| [(); 1000]);
145 assert_trusted_len(&iter);
146 assert_eq!(iter.size_hint(), (3000, Some(3000)));
148 let iter = [(), ()].iter().flat_map(|_| &a);
149 assert_trusted_len(&iter);
150 assert_eq!(iter.size_hint(), (20, Some(20)));