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
new<I>(iter: I) -> (Tee<I>, Tee<I>) where I: Iterator28 pub fn new<I>(iter: I) -> (Tee<I>, Tee<I>)
29 where I: Iterator
30 {
31 let buffer = TeeBuffer{backlog: VecDeque::new(), 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;
next(&mut self) -> Option<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
size_hint(&self) -> (usize, Option<usize>)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 {}
79