1 //! A variant of `SortedMap` that preserves insertion order.
3 use std::borrow::Borrow;
4 use std::hash::{Hash, Hasher};
5 use std::iter::FromIterator;
7 use crate::stable_hasher::{HashStable, StableHasher};
8 use rustc_index::vec::{Idx, IndexVec};
10 /// An indexed multi-map that preserves insertion order while permitting both `O(log n)` lookup of
11 /// an item by key and `O(1)` lookup by index.
13 /// This data structure is a hybrid of an [`IndexVec`] and a [`SortedMap`]. Like `IndexVec`,
14 /// `SortedIndexMultiMap` assigns a typed index to each item while preserving insertion order.
15 /// Like `SortedMap`, `SortedIndexMultiMap` has efficient lookup of items by key. However, this
16 /// is accomplished by sorting an array of item indices instead of the items themselves.
18 /// Unlike `SortedMap`, this data structure can hold multiple equivalent items at once, so the
19 /// `get_by_key` method and its variants return an iterator instead of an `Option`. Equivalent
20 /// items will be yielded in insertion order.
22 /// Unlike a general-purpose map like `BTreeSet` or `HashSet`, `SortedMap` and
23 /// `SortedIndexMultiMap` require `O(n)` time to insert a single item. This is because we may need
24 /// to insert into the middle of the sorted array. Users should avoid mutating this data structure
27 /// [`IndexVec`]: ../../rustc_index/vec/struct.IndexVec.html
28 /// [`SortedMap`]: ../sorted_map/struct.SortedMap.html
29 #[derive(Clone, Debug)]
30 pub struct SortedIndexMultiMap<I: Idx, K, V> {
31 /// The elements of the map in insertion order.
32 items: IndexVec<I, (K, V)>,
34 /// Indices of the items in the set, sorted by the item's key.
35 idx_sorted_by_item_key: Vec<I>,
38 impl<I: Idx, K: Ord, V> SortedIndexMultiMap<I, K, V> {
39 pub fn new() -> Self {
40 SortedIndexMultiMap { items: IndexVec::new(), idx_sorted_by_item_key: Vec::new() }
43 pub fn len(&self) -> usize {
47 pub fn is_empty(&self) -> bool {
51 /// Returns an iterator over the items in the map in insertion order.
52 pub fn into_iter(self) -> impl DoubleEndedIterator<Item = (K, V)> {
53 self.items.into_iter()
56 /// Returns an iterator over the items in the map in insertion order along with their indices.
57 pub fn into_iter_enumerated(self) -> impl DoubleEndedIterator<Item = (I, (K, V))> {
58 self.items.into_iter_enumerated()
61 /// Returns an iterator over the items in the map in insertion order.
62 pub fn iter(&self) -> impl '_ + DoubleEndedIterator<Item = (&K, &V)> {
63 self.items.iter().map(|(ref k, ref v)| (k, v))
66 /// Returns an iterator over the items in the map in insertion order along with their indices.
67 pub fn iter_enumerated(&self) -> impl '_ + DoubleEndedIterator<Item = (I, (&K, &V))> {
68 self.items.iter_enumerated().map(|(i, (ref k, ref v))| (i, (k, v)))
71 /// Returns the item in the map with the given index.
72 pub fn get(&self, idx: I) -> Option<&(K, V)> {
76 /// Returns an iterator over the items in the map that are equal to `key`.
78 /// If there are multiple items that are equivalent to `key`, they will be yielded in
80 pub fn get_by_key<Q: 'a>(&'a self, key: &Q) -> impl 'a + Iterator<Item = &'a V>
85 self.get_by_key_enumerated(key).map(|(_, v)| v)
88 /// Returns an iterator over the items in the map that are equal to `key` along with their
91 /// If there are multiple items that are equivalent to `key`, they will be yielded in
93 pub fn get_by_key_enumerated<Q>(&self, key: &Q) -> impl '_ + Iterator<Item = (I, &V)>
98 // FIXME: This should be in the standard library as `equal_range`. See rust-lang/rfcs#2184.
99 match self.binary_search_idx(key) {
100 Err(_) => self.idxs_to_items_enumerated(&[]),
103 let start = self.find_lower_bound(key, idx);
104 let end = self.find_upper_bound(key, idx);
105 self.idxs_to_items_enumerated(&self.idx_sorted_by_item_key[start..end])
110 fn binary_search_idx<Q>(&self, key: &Q) -> Result<usize, usize>
115 self.idx_sorted_by_item_key.binary_search_by(|&idx| self.items[idx].0.borrow().cmp(key))
118 /// Returns the index into the `idx_sorted_by_item_key` array of the first item equal to
121 /// `initial` must be an index into that same array for an item that is equal to `key`.
122 fn find_lower_bound<Q>(&self, key: &Q, initial: usize) -> usize
127 debug_assert!(self.items[self.idx_sorted_by_item_key[initial]].0.borrow() == key);
129 // FIXME: At present, this uses linear search, meaning lookup is only `O(log n)` if duplicate
130 // entries are rare. It would be better to start with a linear search for the common case but
131 // fall back to an exponential search if many duplicates are found. This applies to
132 // `upper_bound` as well.
133 let mut start = initial;
134 while start != 0 && self.items[self.idx_sorted_by_item_key[start - 1]].0.borrow() == key {
141 /// Returns the index into the `idx_sorted_by_item_key` array of the first item greater than
142 /// `key`, or `self.len()` if no such item exists.
144 /// `initial` must be an index into that same array for an item that is equal to `key`.
145 fn find_upper_bound<Q>(&self, key: &Q, initial: usize) -> usize
150 debug_assert!(self.items[self.idx_sorted_by_item_key[initial]].0.borrow() == key);
152 // See the FIXME for `find_lower_bound`.
153 let mut end = initial + 1;
154 let len = self.items.len();
155 while end < len && self.items[self.idx_sorted_by_item_key[end]].0.borrow() == key {
162 fn idxs_to_items_enumerated(&'a self, idxs: &'a [I]) -> impl 'a + Iterator<Item = (I, &'a V)> {
163 idxs.iter().map(move |&idx| (idx, &self.items[idx].1))
167 impl<I: Idx, K: Eq, V: Eq> Eq for SortedIndexMultiMap<I, K, V> {}
168 impl<I: Idx, K: PartialEq, V: PartialEq> PartialEq for SortedIndexMultiMap<I, K, V> {
169 fn eq(&self, other: &Self) -> bool {
170 // No need to compare the sorted index. If the items are the same, the index will be too.
171 self.items == other.items
175 impl<I: Idx, K, V> Hash for SortedIndexMultiMap<I, K, V>
180 fn hash<H: Hasher>(&self, hasher: &mut H) {
181 self.items.hash(hasher)
184 impl<I: Idx, K, V, C> HashStable<C> for SortedIndexMultiMap<I, K, V>
189 fn hash_stable(&self, ctx: &mut C, hasher: &mut StableHasher) {
190 self.items.hash_stable(ctx, hasher)
194 impl<I: Idx, K: Ord, V> FromIterator<(K, V)> for SortedIndexMultiMap<I, K, V> {
195 fn from_iter<J>(iter: J) -> Self
197 J: IntoIterator<Item = (K, V)>,
199 let items = IndexVec::from_iter(iter);
200 let mut idx_sorted_by_item_key: Vec<_> = items.indices().collect();
202 // `sort_by_key` is stable, so insertion order is preserved for duplicate items.
203 idx_sorted_by_item_key.sort_by_key(|&idx| &items[idx].0);
205 SortedIndexMultiMap { items, idx_sorted_by_item_key }
209 impl<I: Idx, K, V> std::ops::Index<I> for SortedIndexMultiMap<I, K, V> {
212 fn index(&self, idx: I) -> &Self::Output {