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532ac7d7 XL |
1 | use super::size_hint; |
2 | ||
3 | use std::cell::RefCell; | |
4 | use std::collections::VecDeque; | |
5 | use std::rc::Rc; | |
6 | ||
7 | /// Common buffer object for the two tee halves | |
8 | #[derive(Debug)] | |
9 | struct TeeBuffer<A, I> { | |
10 | backlog: VecDeque<A>, | |
11 | iter: I, | |
12 | /// The owner field indicates which id should read from the backlog | |
13 | owner: bool, | |
14 | } | |
15 | ||
16 | /// One half of an iterator pair where both return the same elements. | |
17 | /// | |
18 | /// See [`.tee()`](../trait.Itertools.html#method.tee) for more information. | |
19 | #[must_use = "iterator adaptors are lazy and do nothing unless consumed"] | |
20 | #[derive(Debug)] | |
21 | pub struct Tee<I> | |
22 | where I: Iterator | |
23 | { | |
24 | rcbuffer: Rc<RefCell<TeeBuffer<I::Item, I>>>, | |
25 | id: bool, | |
26 | } | |
27 | ||
28 | pub fn new<I>(iter: I) -> (Tee<I>, Tee<I>) | |
29 | where I: Iterator | |
30 | { | |
31 | let buffer = TeeBuffer{backlog: VecDeque::new(), iter: iter, owner: false}; | |
32 | let t1 = Tee{rcbuffer: Rc::new(RefCell::new(buffer)), id: true}; | |
33 | let t2 = Tee{rcbuffer: t1.rcbuffer.clone(), id: false}; | |
34 | (t1, t2) | |
35 | } | |
36 | ||
37 | impl<I> Iterator for Tee<I> | |
38 | where I: Iterator, | |
39 | I::Item: Clone | |
40 | { | |
41 | type Item = I::Item; | |
42 | fn next(&mut self) -> Option<I::Item> { | |
43 | // .borrow_mut may fail here -- but only if the user has tied some kind of weird | |
44 | // knot where the iterator refers back to itself. | |
45 | let mut buffer = self.rcbuffer.borrow_mut(); | |
46 | if buffer.owner == self.id { | |
47 | match buffer.backlog.pop_front() { | |
48 | None => {} | |
49 | some_elt => return some_elt, | |
50 | } | |
51 | } | |
52 | match buffer.iter.next() { | |
53 | None => None, | |
54 | Some(elt) => { | |
55 | buffer.backlog.push_back(elt.clone()); | |
56 | buffer.owner = !self.id; | |
57 | Some(elt) | |
58 | } | |
59 | } | |
60 | } | |
61 | ||
62 | fn size_hint(&self) -> (usize, Option<usize>) { | |
63 | let buffer = self.rcbuffer.borrow(); | |
64 | let sh = buffer.iter.size_hint(); | |
65 | ||
66 | if buffer.owner == self.id { | |
67 | let log_len = buffer.backlog.len(); | |
68 | size_hint::add_scalar(sh, log_len) | |
69 | } else { | |
70 | sh | |
71 | } | |
72 | } | |
73 | } | |
74 | ||
75 | impl<I> ExactSizeIterator for Tee<I> | |
76 | where I: ExactSizeIterator, | |
77 | I::Item: Clone | |
78 | {} |