1mod cursor;
2
3use arrayvec::ArrayVec;
4pub use cursor::Cursor;
5pub use cursor::FilterCursor;
6use std::{fmt, iter::FromIterator, ops::AddAssign, sync::Arc};
7
8#[cfg(test)]
9const TREE_BASE: usize = 2;
10#[cfg(not(test))]
11const TREE_BASE: usize = 6;
12
13pub trait Item: Clone + fmt::Debug {
14 type Summary: for<'a> AddAssign<&'a Self::Summary> + Default + Clone + fmt::Debug;
15
16 fn summary(&self) -> Self::Summary;
17}
18
19pub trait KeyedItem: Item {
20 type Key: for<'a> Dimension<'a, Self::Summary> + Ord;
21
22 fn key(&self) -> Self::Key;
23}
24
25pub trait Dimension<'a, Summary: Default>: 'a + Clone + fmt::Debug + Default {
26 fn add_summary(&mut self, summary: &'a Summary);
27}
28
29impl<'a, T: Default> Dimension<'a, T> for () {
30 fn add_summary(&mut self, _: &'a T) {}
31}
32
33#[derive(Copy, Clone, Eq, PartialEq)]
34pub enum SeekBias {
35 Left,
36 Right,
37}
38
39#[derive(Debug, Clone)]
40pub struct SumTree<T: Item>(Arc<Node<T>>);
41
42impl<T: Item> SumTree<T> {
43 pub fn new() -> Self {
44 SumTree(Arc::new(Node::Leaf {
45 summary: T::Summary::default(),
46 items: ArrayVec::new(),
47 item_summaries: ArrayVec::new(),
48 }))
49 }
50
51 pub fn from_item(item: T) -> Self {
52 let mut tree = Self::new();
53 tree.push(item);
54 tree
55 }
56
57 #[allow(unused)]
58 pub fn items(&self) -> Vec<T> {
59 let mut cursor = self.cursor::<(), ()>();
60 cursor.descend_to_first_item(self, |_| true);
61 cursor.cloned().collect()
62 }
63
64 pub fn cursor<'a, S, U>(&'a self) -> Cursor<T, S, U>
65 where
66 S: Dimension<'a, T::Summary>,
67 U: Dimension<'a, T::Summary>,
68 {
69 Cursor::new(self)
70 }
71
72 pub fn filter<'a, F, U>(&'a self, filter_node: F) -> FilterCursor<F, T, U>
73 where
74 F: Fn(&T::Summary) -> bool,
75 U: Dimension<'a, T::Summary>,
76 {
77 FilterCursor::new(self, filter_node)
78 }
79
80 #[allow(dead_code)]
81 pub fn first(&self) -> Option<&T> {
82 self.leftmost_leaf().0.items().first()
83 }
84
85 pub fn last(&self) -> Option<&T> {
86 self.rightmost_leaf().0.items().last()
87 }
88
89 pub fn extent<'a, D: Dimension<'a, T::Summary>>(&'a self) -> D {
90 let mut extent = D::default();
91 match self.0.as_ref() {
92 Node::Internal { summary, .. } | Node::Leaf { summary, .. } => {
93 extent.add_summary(summary)
94 }
95 }
96 extent
97 }
98
99 pub fn summary(&self) -> T::Summary {
100 match self.0.as_ref() {
101 Node::Internal { summary, .. } => summary.clone(),
102 Node::Leaf { summary, .. } => summary.clone(),
103 }
104 }
105
106 pub fn is_empty(&self) -> bool {
107 match self.0.as_ref() {
108 Node::Internal { .. } => false,
109 Node::Leaf { items, .. } => items.is_empty(),
110 }
111 }
112
113 pub fn extend<I>(&mut self, iter: I)
114 where
115 I: IntoIterator<Item = T>,
116 {
117 let mut leaf: Option<Node<T>> = None;
118
119 for item in iter {
120 if leaf.is_some() && leaf.as_ref().unwrap().items().len() == 2 * TREE_BASE {
121 self.push_tree(SumTree(Arc::new(leaf.take().unwrap())));
122 }
123
124 if leaf.is_none() {
125 leaf = Some(Node::Leaf::<T> {
126 summary: T::Summary::default(),
127 items: ArrayVec::new(),
128 item_summaries: ArrayVec::new(),
129 });
130 }
131
132 if let Some(Node::Leaf {
133 summary,
134 items,
135 item_summaries,
136 }) = leaf.as_mut()
137 {
138 let item_summary = item.summary();
139 *summary += &item_summary;
140 items.push(item);
141 item_summaries.push(item_summary);
142 } else {
143 unreachable!()
144 }
145 }
146
147 if leaf.is_some() {
148 self.push_tree(SumTree(Arc::new(leaf.take().unwrap())));
149 }
150 }
151
152 pub fn push(&mut self, item: T) {
153 let summary = item.summary();
154 self.push_tree(SumTree::from_child_trees(vec![SumTree(Arc::new(
155 Node::Leaf {
156 summary: summary.clone(),
157 items: ArrayVec::from_iter(Some(item)),
158 item_summaries: ArrayVec::from_iter(Some(summary)),
159 },
160 ))]))
161 }
162
163 pub fn push_tree(&mut self, other: Self) {
164 let other_node = other.0.clone();
165 if !other_node.is_leaf() || other_node.items().len() > 0 {
166 if self.0.height() < other_node.height() {
167 for tree in other_node.child_trees() {
168 self.push_tree(tree.clone());
169 }
170 } else if let Some(split_tree) = self.push_tree_recursive(other) {
171 *self = Self::from_child_trees(vec![self.clone(), split_tree]);
172 }
173 }
174 }
175
176 fn push_tree_recursive(&mut self, other: SumTree<T>) -> Option<SumTree<T>> {
177 match Arc::make_mut(&mut self.0) {
178 Node::Internal {
179 height,
180 summary,
181 child_summaries,
182 child_trees,
183 ..
184 } => {
185 let other_node = other.0.clone();
186 *summary += other_node.summary();
187
188 let height_delta = *height - other_node.height();
189 let mut summaries_to_append = ArrayVec::<[T::Summary; 2 * TREE_BASE]>::new();
190 let mut trees_to_append = ArrayVec::<[SumTree<T>; 2 * TREE_BASE]>::new();
191 if height_delta == 0 {
192 summaries_to_append.extend(other_node.child_summaries().iter().cloned());
193 trees_to_append.extend(other_node.child_trees().iter().cloned());
194 } else if height_delta == 1 && !other_node.is_underflowing() {
195 summaries_to_append.push(other_node.summary().clone());
196 trees_to_append.push(other)
197 } else {
198 let tree_to_append = child_trees.last_mut().unwrap().push_tree_recursive(other);
199 *child_summaries.last_mut().unwrap() =
200 child_trees.last().unwrap().0.summary().clone();
201
202 if let Some(split_tree) = tree_to_append {
203 summaries_to_append.push(split_tree.0.summary().clone());
204 trees_to_append.push(split_tree);
205 }
206 }
207
208 let child_count = child_trees.len() + trees_to_append.len();
209 if child_count > 2 * TREE_BASE {
210 let left_summaries: ArrayVec<_>;
211 let right_summaries: ArrayVec<_>;
212 let left_trees;
213 let right_trees;
214
215 let midpoint = (child_count + child_count % 2) / 2;
216 {
217 let mut all_summaries = child_summaries
218 .iter()
219 .chain(summaries_to_append.iter())
220 .cloned();
221 left_summaries = all_summaries.by_ref().take(midpoint).collect();
222 right_summaries = all_summaries.collect();
223 let mut all_trees =
224 child_trees.iter().chain(trees_to_append.iter()).cloned();
225 left_trees = all_trees.by_ref().take(midpoint).collect();
226 right_trees = all_trees.collect();
227 }
228 *summary = sum(left_summaries.iter());
229 *child_summaries = left_summaries;
230 *child_trees = left_trees;
231
232 Some(SumTree(Arc::new(Node::Internal {
233 height: *height,
234 summary: sum(right_summaries.iter()),
235 child_summaries: right_summaries,
236 child_trees: right_trees,
237 })))
238 } else {
239 child_summaries.extend(summaries_to_append);
240 child_trees.extend(trees_to_append);
241 None
242 }
243 }
244 Node::Leaf {
245 summary,
246 items,
247 item_summaries,
248 } => {
249 let other_node = other.0;
250
251 let child_count = items.len() + other_node.items().len();
252 if child_count > 2 * TREE_BASE {
253 let left_items;
254 let right_items;
255 let left_summaries;
256 let right_summaries: ArrayVec<[T::Summary; 2 * TREE_BASE]>;
257
258 let midpoint = (child_count + child_count % 2) / 2;
259 {
260 let mut all_items = items.iter().chain(other_node.items().iter()).cloned();
261 left_items = all_items.by_ref().take(midpoint).collect();
262 right_items = all_items.collect();
263
264 let mut all_summaries = item_summaries
265 .iter()
266 .chain(other_node.child_summaries())
267 .cloned();
268 left_summaries = all_summaries.by_ref().take(midpoint).collect();
269 right_summaries = all_summaries.collect();
270 }
271 *items = left_items;
272 *item_summaries = left_summaries;
273 *summary = sum(item_summaries.iter());
274 Some(SumTree(Arc::new(Node::Leaf {
275 items: right_items,
276 summary: sum(right_summaries.iter()),
277 item_summaries: right_summaries,
278 })))
279 } else {
280 *summary += other_node.summary();
281 items.extend(other_node.items().iter().cloned());
282 item_summaries.extend(other_node.child_summaries().iter().cloned());
283 None
284 }
285 }
286 }
287 }
288
289 fn from_child_trees(child_trees: Vec<SumTree<T>>) -> Self {
290 let height = child_trees[0].0.height() + 1;
291 let mut child_summaries = ArrayVec::new();
292 for child in &child_trees {
293 child_summaries.push(child.0.summary().clone());
294 }
295 let summary = sum(child_summaries.iter());
296 SumTree(Arc::new(Node::Internal {
297 height,
298 summary,
299 child_summaries,
300 child_trees: ArrayVec::from_iter(child_trees),
301 }))
302 }
303
304 fn leftmost_leaf(&self) -> &Self {
305 match *self.0 {
306 Node::Leaf { .. } => self,
307 Node::Internal {
308 ref child_trees, ..
309 } => child_trees.first().unwrap().leftmost_leaf(),
310 }
311 }
312
313 fn rightmost_leaf(&self) -> &Self {
314 match *self.0 {
315 Node::Leaf { .. } => self,
316 Node::Internal {
317 ref child_trees, ..
318 } => child_trees.last().unwrap().rightmost_leaf(),
319 }
320 }
321}
322
323impl<T: KeyedItem> SumTree<T> {
324 #[allow(unused)]
325 pub fn insert(&mut self, item: T) {
326 *self = {
327 let mut cursor = self.cursor::<T::Key, ()>();
328 let mut new_tree = cursor.slice(&item.key(), SeekBias::Left);
329 new_tree.push(item);
330 new_tree.push_tree(cursor.suffix());
331 new_tree
332 };
333 }
334
335 pub fn edit(&mut self, edits: &mut [Edit<T>]) {
336 if edits.is_empty() {
337 return;
338 }
339
340 edits.sort_unstable_by_key(|item| item.key());
341
342 *self = {
343 let mut cursor = self.cursor::<T::Key, ()>();
344 let mut new_tree = SumTree::new();
345 let mut buffered_items = Vec::new();
346
347 cursor.seek(&T::Key::default(), SeekBias::Left);
348 for edit in edits {
349 let new_key = edit.key();
350 let mut old_item = cursor.item();
351
352 if old_item
353 .as_ref()
354 .map_or(false, |old_item| old_item.key() < new_key)
355 {
356 new_tree.extend(buffered_items.drain(..));
357 let slice = cursor.slice(&new_key, SeekBias::Left);
358 new_tree.push_tree(slice);
359 old_item = cursor.item();
360 }
361 if old_item.map_or(false, |old_item| old_item.key() == new_key) {
362 cursor.next();
363 }
364 match edit {
365 Edit::Insert(item) => {
366 buffered_items.push(item.clone());
367 }
368 }
369 }
370
371 new_tree.extend(buffered_items);
372 new_tree.push_tree(cursor.suffix());
373 new_tree
374 };
375 }
376
377 pub fn get(&self, key: &T::Key) -> Option<&T> {
378 let mut cursor = self.cursor::<T::Key, ()>();
379 if cursor.seek(key, SeekBias::Left) {
380 cursor.item()
381 } else {
382 None
383 }
384 }
385}
386
387impl<T: Item> Default for SumTree<T> {
388 fn default() -> Self {
389 Self::new()
390 }
391}
392
393#[derive(Clone, Debug)]
394pub enum Node<T: Item> {
395 Internal {
396 height: u8,
397 summary: T::Summary,
398 child_summaries: ArrayVec<[T::Summary; 2 * TREE_BASE]>,
399 child_trees: ArrayVec<[SumTree<T>; 2 * TREE_BASE]>,
400 },
401 Leaf {
402 summary: T::Summary,
403 items: ArrayVec<[T; 2 * TREE_BASE]>,
404 item_summaries: ArrayVec<[T::Summary; 2 * TREE_BASE]>,
405 },
406}
407
408impl<T: Item> Node<T> {
409 fn is_leaf(&self) -> bool {
410 match self {
411 Node::Leaf { .. } => true,
412 _ => false,
413 }
414 }
415
416 fn height(&self) -> u8 {
417 match self {
418 Node::Internal { height, .. } => *height,
419 Node::Leaf { .. } => 0,
420 }
421 }
422
423 fn summary(&self) -> &T::Summary {
424 match self {
425 Node::Internal { summary, .. } => summary,
426 Node::Leaf { summary, .. } => summary,
427 }
428 }
429
430 fn child_summaries(&self) -> &[T::Summary] {
431 match self {
432 Node::Internal {
433 child_summaries, ..
434 } => child_summaries.as_slice(),
435 Node::Leaf { item_summaries, .. } => item_summaries.as_slice(),
436 }
437 }
438
439 fn child_trees(&self) -> &ArrayVec<[SumTree<T>; 2 * TREE_BASE]> {
440 match self {
441 Node::Internal { child_trees, .. } => child_trees,
442 Node::Leaf { .. } => panic!("Leaf nodes have no child trees"),
443 }
444 }
445
446 fn items(&self) -> &ArrayVec<[T; 2 * TREE_BASE]> {
447 match self {
448 Node::Leaf { items, .. } => items,
449 Node::Internal { .. } => panic!("Internal nodes have no items"),
450 }
451 }
452
453 fn is_underflowing(&self) -> bool {
454 match self {
455 Node::Internal { child_trees, .. } => child_trees.len() < TREE_BASE,
456 Node::Leaf { items, .. } => items.len() < TREE_BASE,
457 }
458 }
459}
460
461#[derive(Debug)]
462pub enum Edit<T: KeyedItem> {
463 Insert(T),
464}
465
466impl<T: KeyedItem> Edit<T> {
467 fn key(&self) -> T::Key {
468 match self {
469 Edit::Insert(item) => item.key(),
470 }
471 }
472}
473
474fn sum<'a, T, I>(iter: I) -> T
475where
476 T: 'a + Default + AddAssign<&'a T>,
477 I: Iterator<Item = &'a T>,
478{
479 let mut sum = T::default();
480 for value in iter {
481 sum += value;
482 }
483 sum
484}
485
486#[cfg(test)]
487mod tests {
488 use super::*;
489 use std::ops::Add;
490
491 #[test]
492 fn test_extend_and_push_tree() {
493 let mut tree1 = SumTree::new();
494 tree1.extend(0..20);
495
496 let mut tree2 = SumTree::new();
497 tree2.extend(50..100);
498
499 tree1.push_tree(tree2);
500 assert_eq!(tree1.items(), (0..20).chain(50..100).collect::<Vec<u8>>());
501 }
502
503 #[test]
504 fn test_random() {
505 for seed in 0..100 {
506 use rand::{distributions, prelude::*};
507
508 let rng = &mut StdRng::seed_from_u64(seed);
509
510 let mut tree = SumTree::<u8>::new();
511 let count = rng.gen_range(0..10);
512 tree.extend(rng.sample_iter(distributions::Standard).take(count));
513
514 for _ in 0..5 {
515 let splice_end = rng.gen_range(0..tree.extent::<Count>().0 + 1);
516 let splice_start = rng.gen_range(0..splice_end + 1);
517 let count = rng.gen_range(0..3);
518 let tree_end = tree.extent::<Count>();
519 let new_items = rng
520 .sample_iter(distributions::Standard)
521 .take(count)
522 .collect::<Vec<u8>>();
523
524 let mut reference_items = tree.items();
525 reference_items.splice(splice_start..splice_end, new_items.clone());
526
527 tree = {
528 let mut cursor = tree.cursor::<Count, ()>();
529 let mut new_tree = cursor.slice(&Count(splice_start), SeekBias::Right);
530 new_tree.extend(new_items);
531 cursor.seek(&Count(splice_end), SeekBias::Right);
532 new_tree.push_tree(cursor.slice(&tree_end, SeekBias::Right));
533 new_tree
534 };
535
536 assert_eq!(tree.items(), reference_items);
537
538 let mut filter_cursor = tree.filter::<_, Count>(|summary| summary.contains_even);
539 let mut reference_filter = tree
540 .items()
541 .into_iter()
542 .enumerate()
543 .filter(|(_, item)| (item & 1) == 0);
544 while let Some(actual_item) = filter_cursor.item() {
545 let (reference_index, reference_item) = reference_filter.next().unwrap();
546 assert_eq!(actual_item, &reference_item);
547 assert_eq!(filter_cursor.start().0, reference_index);
548 filter_cursor.next();
549 }
550 assert!(reference_filter.next().is_none());
551
552 let mut pos = rng.gen_range(0..tree.extent::<Count>().0 + 1);
553 let mut before_start = false;
554 let mut cursor = tree.cursor::<Count, Count>();
555 cursor.seek(&Count(pos), SeekBias::Right);
556
557 for i in 0..10 {
558 assert_eq!(cursor.start().0, pos);
559
560 if pos > 0 {
561 assert_eq!(cursor.prev_item().unwrap(), &reference_items[pos - 1]);
562 } else {
563 assert_eq!(cursor.prev_item(), None);
564 }
565
566 if pos < reference_items.len() && !before_start {
567 assert_eq!(cursor.item().unwrap(), &reference_items[pos]);
568 } else {
569 assert_eq!(cursor.item(), None);
570 }
571
572 if i < 5 {
573 cursor.next();
574 if pos < reference_items.len() {
575 pos += 1;
576 before_start = false;
577 }
578 } else {
579 cursor.prev();
580 if pos == 0 {
581 before_start = true;
582 }
583 pos = pos.saturating_sub(1);
584 }
585 }
586 }
587
588 for _ in 0..10 {
589 let end = rng.gen_range(0..tree.extent::<Count>().0 + 1);
590 let start = rng.gen_range(0..end + 1);
591 let start_bias = if rng.gen() {
592 SeekBias::Left
593 } else {
594 SeekBias::Right
595 };
596 let end_bias = if rng.gen() {
597 SeekBias::Left
598 } else {
599 SeekBias::Right
600 };
601
602 let mut cursor = tree.cursor::<Count, ()>();
603 cursor.seek(&Count(start), start_bias);
604 let slice = cursor.slice(&Count(end), end_bias);
605
606 cursor.seek(&Count(start), start_bias);
607 let summary = cursor.summary::<Sum>(&Count(end), end_bias);
608
609 assert_eq!(summary, slice.summary().sum);
610 }
611 }
612 }
613
614 #[test]
615 fn test_cursor() {
616 // Empty tree
617 let tree = SumTree::<u8>::new();
618 let mut cursor = tree.cursor::<Count, Sum>();
619 assert_eq!(
620 cursor.slice(&Count(0), SeekBias::Right).items(),
621 Vec::<u8>::new()
622 );
623 assert_eq!(cursor.item(), None);
624 assert_eq!(cursor.prev_item(), None);
625 assert_eq!(cursor.start(), &Sum(0));
626
627 // Single-element tree
628 let mut tree = SumTree::<u8>::new();
629 tree.extend(vec![1]);
630 let mut cursor = tree.cursor::<Count, Sum>();
631 assert_eq!(
632 cursor.slice(&Count(0), SeekBias::Right).items(),
633 Vec::<u8>::new()
634 );
635 assert_eq!(cursor.item(), Some(&1));
636 assert_eq!(cursor.prev_item(), None);
637 assert_eq!(cursor.start(), &Sum(0));
638
639 cursor.next();
640 assert_eq!(cursor.item(), None);
641 assert_eq!(cursor.prev_item(), Some(&1));
642 assert_eq!(cursor.start(), &Sum(1));
643
644 cursor.prev();
645 assert_eq!(cursor.item(), Some(&1));
646 assert_eq!(cursor.prev_item(), None);
647 assert_eq!(cursor.start(), &Sum(0));
648
649 let mut cursor = tree.cursor::<Count, Sum>();
650 assert_eq!(cursor.slice(&Count(1), SeekBias::Right).items(), [1]);
651 assert_eq!(cursor.item(), None);
652 assert_eq!(cursor.prev_item(), Some(&1));
653 assert_eq!(cursor.start(), &Sum(1));
654
655 cursor.seek(&Count(0), SeekBias::Right);
656 assert_eq!(
657 cursor
658 .slice(&tree.extent::<Count>(), SeekBias::Right)
659 .items(),
660 [1]
661 );
662 assert_eq!(cursor.item(), None);
663 assert_eq!(cursor.prev_item(), Some(&1));
664 assert_eq!(cursor.start(), &Sum(1));
665
666 // Multiple-element tree
667 let mut tree = SumTree::new();
668 tree.extend(vec![1, 2, 3, 4, 5, 6]);
669 let mut cursor = tree.cursor::<Count, Sum>();
670
671 assert_eq!(cursor.slice(&Count(2), SeekBias::Right).items(), [1, 2]);
672 assert_eq!(cursor.item(), Some(&3));
673 assert_eq!(cursor.prev_item(), Some(&2));
674 assert_eq!(cursor.start(), &Sum(3));
675
676 cursor.next();
677 assert_eq!(cursor.item(), Some(&4));
678 assert_eq!(cursor.prev_item(), Some(&3));
679 assert_eq!(cursor.start(), &Sum(6));
680
681 cursor.next();
682 assert_eq!(cursor.item(), Some(&5));
683 assert_eq!(cursor.prev_item(), Some(&4));
684 assert_eq!(cursor.start(), &Sum(10));
685
686 cursor.next();
687 assert_eq!(cursor.item(), Some(&6));
688 assert_eq!(cursor.prev_item(), Some(&5));
689 assert_eq!(cursor.start(), &Sum(15));
690
691 cursor.next();
692 cursor.next();
693 assert_eq!(cursor.item(), None);
694 assert_eq!(cursor.prev_item(), Some(&6));
695 assert_eq!(cursor.start(), &Sum(21));
696
697 cursor.prev();
698 assert_eq!(cursor.item(), Some(&6));
699 assert_eq!(cursor.prev_item(), Some(&5));
700 assert_eq!(cursor.start(), &Sum(15));
701
702 cursor.prev();
703 assert_eq!(cursor.item(), Some(&5));
704 assert_eq!(cursor.prev_item(), Some(&4));
705 assert_eq!(cursor.start(), &Sum(10));
706
707 cursor.prev();
708 assert_eq!(cursor.item(), Some(&4));
709 assert_eq!(cursor.prev_item(), Some(&3));
710 assert_eq!(cursor.start(), &Sum(6));
711
712 cursor.prev();
713 assert_eq!(cursor.item(), Some(&3));
714 assert_eq!(cursor.prev_item(), Some(&2));
715 assert_eq!(cursor.start(), &Sum(3));
716
717 cursor.prev();
718 assert_eq!(cursor.item(), Some(&2));
719 assert_eq!(cursor.prev_item(), Some(&1));
720 assert_eq!(cursor.start(), &Sum(1));
721
722 cursor.prev();
723 assert_eq!(cursor.item(), Some(&1));
724 assert_eq!(cursor.prev_item(), None);
725 assert_eq!(cursor.start(), &Sum(0));
726
727 cursor.prev();
728 assert_eq!(cursor.item(), None);
729 assert_eq!(cursor.prev_item(), None);
730 assert_eq!(cursor.start(), &Sum(0));
731
732 cursor.next();
733 assert_eq!(cursor.item(), Some(&1));
734 assert_eq!(cursor.prev_item(), None);
735 assert_eq!(cursor.start(), &Sum(0));
736
737 let mut cursor = tree.cursor::<Count, Sum>();
738 assert_eq!(
739 cursor
740 .slice(&tree.extent::<Count>(), SeekBias::Right)
741 .items(),
742 tree.items()
743 );
744 assert_eq!(cursor.item(), None);
745 assert_eq!(cursor.prev_item(), Some(&6));
746 assert_eq!(cursor.start(), &Sum(21));
747
748 cursor.seek(&Count(3), SeekBias::Right);
749 assert_eq!(
750 cursor
751 .slice(&tree.extent::<Count>(), SeekBias::Right)
752 .items(),
753 [4, 5, 6]
754 );
755 assert_eq!(cursor.item(), None);
756 assert_eq!(cursor.prev_item(), Some(&6));
757 assert_eq!(cursor.start(), &Sum(21));
758
759 // Seeking can bias left or right
760 cursor.seek(&Count(1), SeekBias::Left);
761 assert_eq!(cursor.item(), Some(&1));
762 cursor.seek(&Count(1), SeekBias::Right);
763 assert_eq!(cursor.item(), Some(&2));
764
765 // Slicing without resetting starts from where the cursor is parked at.
766 cursor.seek(&Count(1), SeekBias::Right);
767 assert_eq!(cursor.slice(&Count(3), SeekBias::Right).items(), vec![2, 3]);
768 assert_eq!(cursor.slice(&Count(6), SeekBias::Left).items(), vec![4, 5]);
769 assert_eq!(cursor.slice(&Count(6), SeekBias::Right).items(), vec![6]);
770 }
771
772 #[derive(Clone, Default, Debug)]
773 pub struct IntegersSummary {
774 count: Count,
775 sum: Sum,
776 contains_even: bool,
777 }
778
779 #[derive(Ord, PartialOrd, Default, Eq, PartialEq, Clone, Debug)]
780 struct Count(usize);
781
782 #[derive(Ord, PartialOrd, Default, Eq, PartialEq, Clone, Debug)]
783 struct Sum(usize);
784
785 impl Item for u8 {
786 type Summary = IntegersSummary;
787
788 fn summary(&self) -> Self::Summary {
789 IntegersSummary {
790 count: Count(1),
791 sum: Sum(*self as usize),
792 contains_even: (*self & 1) == 0,
793 }
794 }
795 }
796
797 impl<'a> AddAssign<&'a Self> for IntegersSummary {
798 fn add_assign(&mut self, other: &Self) {
799 self.count.0 += &other.count.0;
800 self.sum.0 += &other.sum.0;
801 self.contains_even |= other.contains_even;
802 }
803 }
804
805 impl<'a> Dimension<'a, IntegersSummary> for Count {
806 fn add_summary(&mut self, summary: &IntegersSummary) {
807 self.0 += summary.count.0;
808 }
809 }
810
811 // impl<'a> Add<&'a Self> for Count {
812 // type Output = Self;
813 //
814 // fn add(mut self, other: &Self) -> Self {
815 // self.0 += other.0;
816 // self
817 // }
818 // }
819
820 impl<'a> Dimension<'a, IntegersSummary> for Sum {
821 fn add_summary(&mut self, summary: &IntegersSummary) {
822 self.0 += summary.sum.0;
823 }
824 }
825
826 impl<'a> Add<&'a Self> for Sum {
827 type Output = Self;
828
829 fn add(mut self, other: &Self) -> Self {
830 self.0 += other.0;
831 self
832 }
833 }
834}