1 use alloc::rc::Rc;
2 use std::cell::RefCell;
3 use std::iter::{FusedIterator, IntoIterator};
4
5 /// A wrapper for `Rc<RefCell<I>>`, that implements the `Iterator` trait.
6 #[derive(Debug)]
7 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
8 pub struct RcIter<I> {
9 /// The boxed iterator.
10 pub rciter: Rc<RefCell<I>>,
11 }
12
13 /// Return an iterator inside a `Rc<RefCell<_>>` wrapper.
14 ///
15 /// The returned `RcIter` can be cloned, and each clone will refer back to the
16 /// same original iterator.
17 ///
18 /// `RcIter` allows doing interesting things like using `.zip()` on an iterator with
19 /// itself, at the cost of runtime borrow checking which may have a performance
20 /// penalty.
21 ///
22 /// Iterator element type is `Self::Item`.
23 ///
24 /// ```
25 /// use itertools::rciter;
26 /// use itertools::zip;
27 ///
28 /// // In this example a range iterator is created and we iterate it using
29 /// // three separate handles (two of them given to zip).
30 /// // We also use the IntoIterator implementation for `&RcIter`.
31 ///
32 /// let mut iter = rciter(0..9);
33 /// let mut z = zip(&iter, &iter);
34 ///
35 /// assert_eq!(z.next(), Some((0, 1)));
36 /// assert_eq!(z.next(), Some((2, 3)));
37 /// assert_eq!(z.next(), Some((4, 5)));
38 /// assert_eq!(iter.next(), Some(6));
39 /// assert_eq!(z.next(), Some((7, 8)));
40 /// assert_eq!(z.next(), None);
41 /// ```
42 ///
43 /// **Panics** in iterator methods if a borrow error is encountered in the
44 /// iterator methods. It can only happen if the `RcIter` is reentered in
45 /// `.next()`, i.e. if it somehow participates in an “iterator knot”
46 /// where it is an adaptor of itself.
rciter<I>(iterable: I) -> RcIter<I::IntoIter> where I: IntoIterator,47 pub fn rciter<I>(iterable: I) -> RcIter<I::IntoIter>
48 where
49 I: IntoIterator,
50 {
51 RcIter {
52 rciter: Rc::new(RefCell::new(iterable.into_iter())),
53 }
54 }
55
56 impl<I> Clone for RcIter<I> {
57 clone_fields!(rciter);
58 }
59
60 impl<A, I> Iterator for RcIter<I>
61 where
62 I: Iterator<Item = A>,
63 {
64 type Item = A;
65 #[inline]
next(&mut self) -> Option<Self::Item>66 fn next(&mut self) -> Option<Self::Item> {
67 self.rciter.borrow_mut().next()
68 }
69
70 #[inline]
size_hint(&self) -> (usize, Option<usize>)71 fn size_hint(&self) -> (usize, Option<usize>) {
72 // To work sanely with other API that assume they own an iterator,
73 // so it can't change in other places, we can't guarantee as much
74 // in our size_hint. Other clones may drain values under our feet.
75 (0, self.rciter.borrow().size_hint().1)
76 }
77 }
78
79 impl<I> DoubleEndedIterator for RcIter<I>
80 where
81 I: DoubleEndedIterator,
82 {
83 #[inline]
next_back(&mut self) -> Option<Self::Item>84 fn next_back(&mut self) -> Option<Self::Item> {
85 self.rciter.borrow_mut().next_back()
86 }
87 }
88
89 /// Return an iterator from `&RcIter<I>` (by simply cloning it).
90 impl<'a, I> IntoIterator for &'a RcIter<I>
91 where
92 I: Iterator,
93 {
94 type Item = I::Item;
95 type IntoIter = RcIter<I>;
96
into_iter(self) -> RcIter<I>97 fn into_iter(self) -> RcIter<I> {
98 self.clone()
99 }
100 }
101
102 impl<A, I> FusedIterator for RcIter<I> where I: FusedIterator<Item = A> {}
103