1use std::fmt;
2use std::iter::FusedIterator;
3
4use crate::size_hint;
5
6#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
7pub struct CoalesceBy<I, F, T>
8where
9 I: Iterator,
10{
11 iter: I,
12 last: Option<T>,
13 f: F,
14}
15
16impl<I: Clone, F: Clone, T: Clone> Clone for CoalesceBy<I, F, T>
17where
18 I: Iterator,
19{
20 clone_fields!(last, iter, f);
21}
22
23impl<I, F, T> fmt::Debug for CoalesceBy<I, F, T>
24where
25 I: Iterator + fmt::Debug,
26 T: fmt::Debug,
27{
28 debug_fmt_fields!(CoalesceBy, iter);
29}
30
31pub trait CoalescePredicate<Item, T> {
32 fn coalesce_pair(&mut self, t: T, item: Item) -> Result<T, (T, T)>;
33}
34
35impl<I, F, T> Iterator for CoalesceBy<I, F, T>
36where
37 I: Iterator,
38 F: CoalescePredicate<I::Item, T>,
39{
40 type Item = T;
41
42 fn next(&mut self) -> Option<Self::Item> {
43 // this fuses the iterator
44 let last = self.last.take()?;
45
46 let self_last = &mut self.last;
47 let self_f = &mut self.f;
48 Some(
49 self.iter
50 .try_fold(last, |last, next| match self_f.coalesce_pair(last, next) {
51 Ok(joined) => Ok(joined),
52 Err((last_, next_)) => {
53 *self_last = Some(next_);
54 Err(last_)
55 }
56 })
57 .unwrap_or_else(|x| x),
58 )
59 }
60
61 fn size_hint(&self) -> (usize, Option<usize>) {
62 let (low, hi) = size_hint::add_scalar(self.iter.size_hint(), self.last.is_some() as usize);
63 ((low > 0) as usize, hi)
64 }
65
66 fn fold<Acc, FnAcc>(self, acc: Acc, mut fn_acc: FnAcc) -> Acc
67 where
68 FnAcc: FnMut(Acc, Self::Item) -> Acc,
69 {
70 if let Some(last) = self.last {
71 let mut f = self.f;
72 let (last, acc) = self.iter.fold((last, acc), |(last, acc), elt| {
73 match f.coalesce_pair(last, elt) {
74 Ok(joined) => (joined, acc),
75 Err((last_, next_)) => (next_, fn_acc(acc, last_)),
76 }
77 });
78 fn_acc(acc, last)
79 } else {
80 acc
81 }
82 }
83}
84
85impl<I: Iterator, F: CoalescePredicate<I::Item, T>, T> FusedIterator for CoalesceBy<I, F, T> {}
86
87/// An iterator adaptor that may join together adjacent elements.
88///
89/// See [`.coalesce()`](crate::Itertools::coalesce) for more information.
90pub type Coalesce<I, F> = CoalesceBy<I, F, <I as Iterator>::Item>;
91
92impl<F, Item, T> CoalescePredicate<Item, T> for F
93where
94 F: FnMut(T, Item) -> Result<T, (T, T)>,
95{
96 fn coalesce_pair(&mut self, t: T, item: Item) -> Result<T, (T, T)> {
97 self(t, item)
98 }
99}
100
101/// Create a new `Coalesce`.
102pub fn coalesce<I, F>(mut iter: I, f: F) -> Coalesce<I, F>
103where
104 I: Iterator,
105{
106 Coalesce {
107 last: iter.next(),
108 iter,
109 f,
110 }
111}
112
113/// An iterator adaptor that removes repeated duplicates, determining equality using a comparison function.
114///
115/// See [`.dedup_by()`](crate::Itertools::dedup_by) or [`.dedup()`](crate::Itertools::dedup) for more information.
116pub type DedupBy<I, Pred> = CoalesceBy<I, DedupPred2CoalescePred<Pred>, <I as Iterator>::Item>;
117
118#[derive(Clone)]
119pub struct DedupPred2CoalescePred<DP>(DP);
120
121impl<DP> fmt::Debug for DedupPred2CoalescePred<DP> {
122 debug_fmt_fields!(DedupPred2CoalescePred,);
123}
124
125pub trait DedupPredicate<T> {
126 // TODO replace by Fn(&T, &T)->bool once Rust supports it
127 fn dedup_pair(&mut self, a: &T, b: &T) -> bool;
128}
129
130impl<DP, T> CoalescePredicate<T, T> for DedupPred2CoalescePred<DP>
131where
132 DP: DedupPredicate<T>,
133{
134 fn coalesce_pair(&mut self, t: T, item: T) -> Result<T, (T, T)> {
135 if self.0.dedup_pair(&t, &item) {
136 Ok(t)
137 } else {
138 Err((t, item))
139 }
140 }
141}
142
143#[derive(Clone, Debug)]
144pub struct DedupEq;
145
146impl<T: PartialEq> DedupPredicate<T> for DedupEq {
147 fn dedup_pair(&mut self, a: &T, b: &T) -> bool {
148 a == b
149 }
150}
151
152impl<T, F: FnMut(&T, &T) -> bool> DedupPredicate<T> for F {
153 fn dedup_pair(&mut self, a: &T, b: &T) -> bool {
154 self(a, b)
155 }
156}
157
158/// Create a new `DedupBy`.
159pub fn dedup_by<I, Pred>(mut iter: I, dedup_pred: Pred) -> DedupBy<I, Pred>
160where
161 I: Iterator,
162{
163 DedupBy {
164 last: iter.next(),
165 iter,
166 f: DedupPred2CoalescePred(dedup_pred),
167 }
168}
169
170/// An iterator adaptor that removes repeated duplicates.
171///
172/// See [`.dedup()`](crate::Itertools::dedup) for more information.
173pub type Dedup<I> = DedupBy<I, DedupEq>;
174
175/// Create a new `Dedup`.
176pub fn dedup<I>(iter: I) -> Dedup<I>
177where
178 I: Iterator,
179{
180 dedup_by(iter, DedupEq)
181}
182
183/// An iterator adaptor that removes repeated duplicates, while keeping a count of how many
184/// repeated elements were present. This will determine equality using a comparison function.
185///
186/// See [`.dedup_by_with_count()`](crate::Itertools::dedup_by_with_count) or
187/// [`.dedup_with_count()`](crate::Itertools::dedup_with_count) for more information.
188pub type DedupByWithCount<I, Pred> =
189 CoalesceBy<I, DedupPredWithCount2CoalescePred<Pred>, (usize, <I as Iterator>::Item)>;
190
191#[derive(Clone, Debug)]
192pub struct DedupPredWithCount2CoalescePred<DP>(DP);
193
194impl<DP, T> CoalescePredicate<T, (usize, T)> for DedupPredWithCount2CoalescePred<DP>
195where
196 DP: DedupPredicate<T>,
197{
198 fn coalesce_pair(
199 &mut self,
200 (c, t): (usize, T),
201 item: T,
202 ) -> Result<(usize, T), ((usize, T), (usize, T))> {
203 if self.0.dedup_pair(&t, &item) {
204 Ok((c + 1, t))
205 } else {
206 Err(((c, t), (1, item)))
207 }
208 }
209}
210
211/// An iterator adaptor that removes repeated duplicates, while keeping a count of how many
212/// repeated elements were present.
213///
214/// See [`.dedup_with_count()`](crate::Itertools::dedup_with_count) for more information.
215pub type DedupWithCount<I> = DedupByWithCount<I, DedupEq>;
216
217/// Create a new `DedupByWithCount`.
218pub fn dedup_by_with_count<I, Pred>(mut iter: I, dedup_pred: Pred) -> DedupByWithCount<I, Pred>
219where
220 I: Iterator,
221{
222 DedupByWithCount {
223 last: iter.next().map(|v| (1, v)),
224 iter,
225 f: DedupPredWithCount2CoalescePred(dedup_pred),
226 }
227}
228
229/// Create a new `DedupWithCount`.
230pub fn dedup_with_count<I>(iter: I) -> DedupWithCount<I>
231where
232 I: Iterator,
233{
234 dedup_by_with_count(iter, DedupEq)
235}
236