1use alloc::rc::Rc;
2use std::cell::RefCell;
3use 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"]
8pub 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.
47pub fn rciter<I>(iterable: I) -> RcIter<I::IntoIter>
48where
49 I: IntoIterator,
50{
51 RcIter {
52 rciter: Rc::new(RefCell::new(iterable.into_iter())),
53 }
54}
55
56impl<I> Clone for RcIter<I> {
57 clone_fields!(rciter);
58}
59
60impl<A, I> Iterator for RcIter<I>
61where
62 I: Iterator<Item = A>,
63{
64 type Item = A;
65 #[inline]
66 fn next(&mut self) -> Option<Self::Item> {
67 self.rciter.borrow_mut().next()
68 }
69
70 #[inline]
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
79impl<I> DoubleEndedIterator for RcIter<I>
80where
81 I: DoubleEndedIterator,
82{
83 #[inline]
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).
90impl<'a, I> IntoIterator for &'a RcIter<I>
91where
92 I: Iterator,
93{
94 type Item = I::Item;
95 type IntoIter = RcIter<I>;
96
97 fn into_iter(self) -> RcIter<I> {
98 self.clone()
99 }
100}
101
102impl<A, I> FusedIterator for RcIter<I> where I: FusedIterator<Item = A> {}
103