alloc/collections/vec_deque/
iter.rs

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1use core::iter::{FusedIterator, TrustedLen, TrustedRandomAccess, TrustedRandomAccessNoCoerce};
2use core::num::NonZero;
3use core::ops::Try;
4use core::{fmt, mem, slice};
5
6/// An iterator over the elements of a `VecDeque`.
7///
8/// This `struct` is created by the [`iter`] method on [`super::VecDeque`]. See its
9/// documentation for more.
10///
11/// [`iter`]: super::VecDeque::iter
12#[stable(feature = "rust1", since = "1.0.0")]
13pub struct Iter<'a, T: 'a> {
14    i1: slice::Iter<'a, T>,
15    i2: slice::Iter<'a, T>,
16}
17
18impl<'a, T> Iter<'a, T> {
19    pub(super) fn new(i1: slice::Iter<'a, T>, i2: slice::Iter<'a, T>) -> Self {
20        Self { i1, i2 }
21    }
22
23    /// Views the underlying data as a pair of subslices of the original data.
24    ///
25    /// The slices contain, in order, the contents of the deque not yet yielded
26    /// by the iterator.
27    ///
28    /// This has the same lifetime as the original `VecDeque`, and so the
29    /// iterator can continue to be used while this exists.
30    ///
31    /// # Examples
32    ///
33    /// ```
34    /// #![feature(vec_deque_iter_as_slices)]
35    ///
36    /// use std::collections::VecDeque;
37    ///
38    /// let mut deque = VecDeque::new();
39    /// deque.push_back(0);
40    /// deque.push_back(1);
41    /// deque.push_back(2);
42    /// deque.push_front(10);
43    /// deque.push_front(9);
44    /// deque.push_front(8);
45    ///
46    /// let mut iter = deque.iter();
47    /// iter.next();
48    /// iter.next_back();
49    ///
50    /// assert_eq!(iter.as_slices(), (&[9, 10][..], &[0, 1][..]));
51    /// ```
52    #[unstable(feature = "vec_deque_iter_as_slices", issue = "123947")]
53    pub fn as_slices(&self) -> (&'a [T], &'a [T]) {
54        (self.i1.as_slice(), self.i2.as_slice())
55    }
56}
57
58#[stable(feature = "collection_debug", since = "1.17.0")]
59impl<T: fmt::Debug> fmt::Debug for Iter<'_, T> {
60    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
61        f.debug_tuple("Iter").field(&self.i1.as_slice()).field(&self.i2.as_slice()).finish()
62    }
63}
64
65#[stable(feature = "default_iters_sequel", since = "1.82.0")]
66impl<T> Default for Iter<'_, T> {
67    /// Creates an empty `vec_deque::Iter`.
68    ///
69    /// ```
70    /// # use std::collections::vec_deque;
71    /// let iter: vec_deque::Iter<'_, u8> = Default::default();
72    /// assert_eq!(iter.len(), 0);
73    /// ```
74    fn default() -> Self {
75        Iter { i1: Default::default(), i2: Default::default() }
76    }
77}
78
79// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
80#[stable(feature = "rust1", since = "1.0.0")]
81impl<T> Clone for Iter<'_, T> {
82    fn clone(&self) -> Self {
83        Iter { i1: self.i1.clone(), i2: self.i2.clone() }
84    }
85}
86
87#[stable(feature = "rust1", since = "1.0.0")]
88impl<'a, T> Iterator for Iter<'a, T> {
89    type Item = &'a T;
90
91    #[inline]
92    fn next(&mut self) -> Option<&'a T> {
93        match self.i1.next() {
94            Some(val) => Some(val),
95            None => {
96                // most of the time, the iterator will either always
97                // call next(), or always call next_back(). By swapping
98                // the iterators once the first one is empty, we ensure
99                // that the first branch is taken as often as possible,
100                // without sacrificing correctness, as i1 is empty anyways
101                mem::swap(&mut self.i1, &mut self.i2);
102                self.i1.next()
103            }
104        }
105    }
106
107    fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
108        let remaining = self.i1.advance_by(n);
109        match remaining {
110            Ok(()) => Ok(()),
111            Err(n) => {
112                mem::swap(&mut self.i1, &mut self.i2);
113                self.i1.advance_by(n.get())
114            }
115        }
116    }
117
118    #[inline]
119    fn size_hint(&self) -> (usize, Option<usize>) {
120        let len = self.len();
121        (len, Some(len))
122    }
123
124    fn fold<Acc, F>(self, accum: Acc, mut f: F) -> Acc
125    where
126        F: FnMut(Acc, Self::Item) -> Acc,
127    {
128        let accum = self.i1.fold(accum, &mut f);
129        self.i2.fold(accum, &mut f)
130    }
131
132    fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R
133    where
134        F: FnMut(B, Self::Item) -> R,
135        R: Try<Output = B>,
136    {
137        let acc = self.i1.try_fold(init, &mut f)?;
138        self.i2.try_fold(acc, &mut f)
139    }
140
141    #[inline]
142    fn last(mut self) -> Option<&'a T> {
143        self.next_back()
144    }
145
146    #[inline]
147    unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item {
148        // Safety: The TrustedRandomAccess contract requires that callers only pass an index
149        // that is in bounds.
150        unsafe {
151            let i1_len = self.i1.len();
152            if idx < i1_len {
153                self.i1.__iterator_get_unchecked(idx)
154            } else {
155                self.i2.__iterator_get_unchecked(idx - i1_len)
156            }
157        }
158    }
159}
160
161#[stable(feature = "rust1", since = "1.0.0")]
162impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
163    #[inline]
164    fn next_back(&mut self) -> Option<&'a T> {
165        match self.i2.next_back() {
166            Some(val) => Some(val),
167            None => {
168                // most of the time, the iterator will either always
169                // call next(), or always call next_back(). By swapping
170                // the iterators once the second one is empty, we ensure
171                // that the first branch is taken as often as possible,
172                // without sacrificing correctness, as i2 is empty anyways
173                mem::swap(&mut self.i1, &mut self.i2);
174                self.i2.next_back()
175            }
176        }
177    }
178
179    fn advance_back_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
180        match self.i2.advance_back_by(n) {
181            Ok(()) => Ok(()),
182            Err(n) => {
183                mem::swap(&mut self.i1, &mut self.i2);
184                self.i2.advance_back_by(n.get())
185            }
186        }
187    }
188
189    fn rfold<Acc, F>(self, accum: Acc, mut f: F) -> Acc
190    where
191        F: FnMut(Acc, Self::Item) -> Acc,
192    {
193        let accum = self.i2.rfold(accum, &mut f);
194        self.i1.rfold(accum, &mut f)
195    }
196
197    fn try_rfold<B, F, R>(&mut self, init: B, mut f: F) -> R
198    where
199        F: FnMut(B, Self::Item) -> R,
200        R: Try<Output = B>,
201    {
202        let acc = self.i2.try_rfold(init, &mut f)?;
203        self.i1.try_rfold(acc, &mut f)
204    }
205}
206
207#[stable(feature = "rust1", since = "1.0.0")]
208impl<T> ExactSizeIterator for Iter<'_, T> {
209    fn len(&self) -> usize {
210        self.i1.len() + self.i2.len()
211    }
212
213    fn is_empty(&self) -> bool {
214        self.i1.is_empty() && self.i2.is_empty()
215    }
216}
217
218#[stable(feature = "fused", since = "1.26.0")]
219impl<T> FusedIterator for Iter<'_, T> {}
220
221#[unstable(feature = "trusted_len", issue = "37572")]
222unsafe impl<T> TrustedLen for Iter<'_, T> {}
223
224#[doc(hidden)]
225#[unstable(feature = "trusted_random_access", issue = "none")]
226unsafe impl<T> TrustedRandomAccess for Iter<'_, T> {}
227
228#[doc(hidden)]
229#[unstable(feature = "trusted_random_access", issue = "none")]
230unsafe impl<T> TrustedRandomAccessNoCoerce for Iter<'_, T> {
231    const MAY_HAVE_SIDE_EFFECT: bool = false;
232}
alloc/collections/vec_deque/iter.rs

alloc/collections/vec_deque/
iter.rs
