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| 1 | +use core::alloc::Allocator; |
| 2 | + |
| 3 | +use crate::alloc::Global; |
| 4 | +use crate::collections::vec_deque::Drain; |
| 5 | +use crate::vec::Vec; |
| 6 | + |
| 7 | +/// A splicing iterator for `VecDeque`. |
| 8 | +/// |
| 9 | +/// This struct is created by [`VecDeque::splice()`][super::VecDeque::splice]. |
| 10 | +/// See its documentation for more. |
| 11 | +/// |
| 12 | +/// # Example |
| 13 | +/// |
| 14 | +/// ``` |
| 15 | +/// # #![feature(deque_extend_front)] |
| 16 | +/// # use std::collections::VecDeque; |
| 17 | +/// |
| 18 | +/// let mut v = VecDeque::from(vec![0, 1, 2]); |
| 19 | +/// let new = [7, 8]; |
| 20 | +/// let iter: std::collections::vec_deque::Splice<'_, _> = v.splice(1.., new); |
| 21 | +/// ``` |
| 22 | +#[unstable(feature = "deque_extend_front", issue = "146975")] |
| 23 | +#[derive(Debug)] |
| 24 | +pub struct Splice< |
| 25 | + 'a, |
| 26 | + I: Iterator + 'a, |
| 27 | + #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator + 'a = Global, |
| 28 | +> { |
| 29 | + pub(super) drain: Drain<'a, I::Item, A>, |
| 30 | + pub(super) replace_with: I, |
| 31 | +} |
| 32 | + |
| 33 | +#[unstable(feature = "deque_extend_front", issue = "146975")] |
| 34 | +impl<I: Iterator, A: Allocator> Iterator for Splice<'_, I, A> { |
| 35 | + type Item = I::Item; |
| 36 | + |
| 37 | + fn next(&mut self) -> Option<Self::Item> { |
| 38 | + self.drain.next() |
| 39 | + } |
| 40 | + |
| 41 | + fn size_hint(&self) -> (usize, Option<usize>) { |
| 42 | + self.drain.size_hint() |
| 43 | + } |
| 44 | +} |
| 45 | + |
| 46 | +#[unstable(feature = "deque_extend_front", issue = "146975")] |
| 47 | +impl<I: Iterator, A: Allocator> DoubleEndedIterator for Splice<'_, I, A> { |
| 48 | + fn next_back(&mut self) -> Option<Self::Item> { |
| 49 | + self.drain.next_back() |
| 50 | + } |
| 51 | +} |
| 52 | + |
| 53 | +#[unstable(feature = "deque_extend_front", issue = "146975")] |
| 54 | +impl<I: Iterator, A: Allocator> ExactSizeIterator for Splice<'_, I, A> {} |
| 55 | + |
| 56 | +// See also: [`crate::vec::Splice`]. |
| 57 | +#[unstable(feature = "deque_extend_front", issue = "146975")] |
| 58 | +impl<I: Iterator, A: Allocator> Drop for Splice<'_, I, A> { |
| 59 | + fn drop(&mut self) { |
| 60 | + // This will set drain.remaining to 0, so its drop won't try to read deallocated memory on |
| 61 | + // drop. |
| 62 | + self.drain.by_ref().for_each(drop); |
| 63 | + |
| 64 | + // At this point draining is done and the only remaining tasks are splicing |
| 65 | + // and moving things into the final place. |
| 66 | + |
| 67 | + unsafe { |
| 68 | + let tail_len = self.drain.tail_len; // #elements behind the drain |
| 69 | + |
| 70 | + if tail_len == 0 { |
| 71 | + self.drain.deque.as_mut().extend(self.replace_with.by_ref()); |
| 72 | + return; |
| 73 | + } |
| 74 | + |
| 75 | + // First fill the range left by drain(). |
| 76 | + if !self.drain.fill(&mut self.replace_with) { |
| 77 | + return; |
| 78 | + } |
| 79 | + |
| 80 | + // There may be more elements. Use the lower bound as an estimate. |
| 81 | + // FIXME: Is the upper bound a better guess? Or something else? |
| 82 | + let (lower_bound, _upper_bound) = self.replace_with.size_hint(); |
| 83 | + if lower_bound > 0 { |
| 84 | + self.drain.move_tail(lower_bound); |
| 85 | + if !self.drain.fill(&mut self.replace_with) { |
| 86 | + return; |
| 87 | + } |
| 88 | + } |
| 89 | + |
| 90 | + // Collect any remaining elements. |
| 91 | + // This is a zero-length vector which does not allocate if `lower_bound` was exact. |
| 92 | + let mut collected = self.replace_with.by_ref().collect::<Vec<I::Item>>().into_iter(); |
| 93 | + // Now we have an exact count. |
| 94 | + if collected.len() > 0 { |
| 95 | + self.drain.move_tail(collected.len()); |
| 96 | + let filled = self.drain.fill(&mut collected); |
| 97 | + debug_assert!(filled); |
| 98 | + debug_assert_eq!(collected.len(), 0); |
| 99 | + } |
| 100 | + } |
| 101 | + // Let `Drain::drop` move the tail back if necessary and restore `deque.len`. |
| 102 | + } |
| 103 | +} |
| 104 | + |
| 105 | +/// Private helper methods for `Splice::drop` |
| 106 | +impl<T, A: Allocator> Drain<'_, T, A> { |
| 107 | + /// The range from `self.deque.len` to `self.deque.len + self.drain_len` contains elements that |
| 108 | + /// have been moved out. |
| 109 | + /// Fill that range as much as possible with new elements from the `replace_with` iterator. |
| 110 | + /// Returns `true` if we filled the entire range. (`replace_with.next()` didn’t return `None`.) |
| 111 | + /// |
| 112 | + /// # Safety |
| 113 | + /// |
| 114 | + /// self.deque must be valid. self.deque.len and self.deque.len + self.drain_len must be less |
| 115 | + /// than twice the deque's capacity. |
| 116 | + unsafe fn fill<I: Iterator<Item = T>>(&mut self, replace_with: &mut I) -> bool { |
| 117 | + let deque = unsafe { self.deque.as_mut() }; |
| 118 | + let range_start = deque.len; |
| 119 | + let range_end = range_start + self.drain_len; |
| 120 | + |
| 121 | + for idx in range_start..range_end { |
| 122 | + if let Some(new_item) = replace_with.next() { |
| 123 | + let index = deque.to_physical_idx(idx); |
| 124 | + unsafe { deque.buffer_write(index, new_item) }; |
| 125 | + deque.len += 1; |
| 126 | + self.drain_len -= 1; |
| 127 | + } else { |
| 128 | + return false; |
| 129 | + } |
| 130 | + } |
| 131 | + true |
| 132 | + } |
| 133 | + |
| 134 | + /// Makes room for inserting more elements before the tail. |
| 135 | + /// |
| 136 | + /// # Safety |
| 137 | + /// |
| 138 | + /// self.deque must be valid. |
| 139 | + unsafe fn move_tail(&mut self, additional: usize) { |
| 140 | + let deque = unsafe { self.deque.as_mut() }; |
| 141 | + let tail_start = deque.len + self.drain_len; |
| 142 | + deque.buf.reserve(tail_start + self.tail_len, additional); |
| 143 | + |
| 144 | + let new_tail_start = tail_start + additional; |
| 145 | + unsafe { |
| 146 | + deque.wrap_copy(tail_start, new_tail_start, self.tail_len); |
| 147 | + } |
| 148 | + self.drain_len += additional; |
| 149 | + } |
| 150 | +} |
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