alloc/collections/vec_deque/
spec_extend.rs

1use core::iter::{Copied, Rev, TrustedLen};
2use core::slice;
3
4use super::{Drain, VecDeque};
5use crate::alloc::Allocator;
6#[cfg(not(test))]
7use crate::vec;
8
9// Specialization trait used for VecDeque::extend
10pub(super) trait SpecExtend<T, I> {
11    fn spec_extend(&mut self, iter: I);
12}
13
14impl<T, I, A: Allocator> SpecExtend<T, I> for VecDeque<T, A>
15where
16    I: Iterator<Item = T>,
17{
18    default fn spec_extend(&mut self, mut iter: I) {
19        // This function should be the moral equivalent of:
20        //
21        // for item in iter {
22        //     self.push_back(item);
23        // }
24
25        while let Some(element) = iter.next() {
26            let (lower, _) = iter.size_hint();
27            self.reserve(lower.saturating_add(1));
28
29            // SAFETY: We just reserved space for at least one element.
30            unsafe { self.push_unchecked(element) };
31
32            // Inner loop to avoid repeatedly calling `reserve`.
33            while self.len < self.capacity() {
34                let Some(element) = iter.next() else {
35                    return;
36                };
37                // SAFETY: The loop condition guarantees that `self.len() < self.capacity()`.
38                unsafe { self.push_unchecked(element) };
39            }
40        }
41    }
42}
43
44impl<T, I, A: Allocator> SpecExtend<T, I> for VecDeque<T, A>
45where
46    I: TrustedLen<Item = T>,
47{
48    default fn spec_extend(&mut self, iter: I) {
49        // This is the case for a TrustedLen iterator.
50        let (low, high) = iter.size_hint();
51        if let Some(additional) = high {
52            debug_assert_eq!(
53                low,
54                additional,
55                "TrustedLen iterator's size hint is not exact: {:?}",
56                (low, high)
57            );
58            self.reserve(additional);
59
60            let written = unsafe {
61                self.write_iter_wrapping(self.to_physical_idx(self.len), iter, additional)
62            };
63
64            debug_assert_eq!(
65                additional, written,
66                "The number of items written to VecDeque doesn't match the TrustedLen size hint"
67            );
68        } else {
69            // Per TrustedLen contract a `None` upper bound means that the iterator length
70            // truly exceeds usize::MAX, which would eventually lead to a capacity overflow anyway.
71            // Since the other branch already panics eagerly (via `reserve()`) we do the same here.
72            // This avoids additional codegen for a fallback code path which would eventually
73            // panic anyway.
74            panic!("capacity overflow");
75        }
76    }
77}
78
79#[cfg(not(test))]
80impl<T, A1: Allocator, A2: Allocator> SpecExtend<T, vec::IntoIter<T, A2>> for VecDeque<T, A1> {
81    fn spec_extend(&mut self, mut iterator: vec::IntoIter<T, A2>) {
82        let slice = iterator.as_slice();
83        self.reserve(slice.len());
84
85        unsafe {
86            self.copy_slice(self.to_physical_idx(self.len), slice);
87            self.len += slice.len();
88        }
89        iterator.forget_remaining_elements();
90    }
91}
92
93impl<'a, T: 'a, I, A: Allocator> SpecExtend<&'a T, I> for VecDeque<T, A>
94where
95    I: Iterator<Item = &'a T>,
96    T: Copy,
97{
98    default fn spec_extend(&mut self, iterator: I) {
99        self.spec_extend(iterator.copied())
100    }
101}
102
103impl<'a, T: 'a, A: Allocator> SpecExtend<&'a T, slice::Iter<'a, T>> for VecDeque<T, A>
104where
105    T: Copy,
106{
107    fn spec_extend(&mut self, iterator: slice::Iter<'a, T>) {
108        let slice = iterator.as_slice();
109        self.reserve(slice.len());
110
111        unsafe {
112            self.copy_slice(self.to_physical_idx(self.len), slice);
113            self.len += slice.len();
114        }
115    }
116}
117
118// Specialization trait used for VecDeque::extend_front
119pub(super) trait SpecExtendFront<T, I> {
120    #[track_caller]
121    fn spec_extend_front(&mut self, iter: I);
122}
123
124impl<T, I, A: Allocator> SpecExtendFront<T, I> for VecDeque<T, A>
125where
126    I: Iterator<Item = T>,
127{
128    #[track_caller]
129    default fn spec_extend_front(&mut self, mut iter: I) {
130        // This function should be the moral equivalent of:
131        //
132        // for item in iter {
133        //     self.push_front(item);
134        // }
135
136        while let Some(element) = iter.next() {
137            let (lower, _) = iter.size_hint();
138            self.reserve(lower.saturating_add(1));
139
140            // SAFETY: We just reserved space for at least one element.
141            unsafe { self.push_front_unchecked(element) };
142
143            // Inner loop to avoid repeatedly calling `reserve`.
144            while self.len < self.capacity() {
145                let Some(element) = iter.next() else {
146                    return;
147                };
148                // SAFETY: The loop condition guarantees that `self.len() < self.capacity()`.
149                unsafe { self.push_front_unchecked(element) };
150            }
151        }
152    }
153}
154
155#[cfg(not(test))]
156impl<T, A1: Allocator, A2: Allocator> SpecExtendFront<T, vec::IntoIter<T, A2>> for VecDeque<T, A1> {
157    #[track_caller]
158    fn spec_extend_front(&mut self, mut iterator: vec::IntoIter<T, A2>) {
159        let slice = iterator.as_slice();
160        self.reserve(slice.len());
161        // SAFETY: `slice.len()` space was just reserved and elements in the slice are forgotten after this call
162        unsafe { prepend_reversed(self, slice) };
163        iterator.forget_remaining_elements();
164    }
165}
166
167#[cfg(not(test))]
168impl<T, A1: Allocator, A2: Allocator> SpecExtendFront<T, Rev<vec::IntoIter<T, A2>>>
169    for VecDeque<T, A1>
170{
171    #[track_caller]
172    fn spec_extend_front(&mut self, iterator: Rev<vec::IntoIter<T, A2>>) {
173        let mut iterator = iterator.into_inner();
174        let slice = iterator.as_slice();
175        self.reserve(slice.len());
176        // SAFETY: `slice.len()` space was just reserved and elements in the slice are forgotten after this call
177        unsafe { prepend(self, slice) };
178        iterator.forget_remaining_elements();
179    }
180}
181
182impl<'a, T, A: Allocator> SpecExtendFront<T, Copied<slice::Iter<'a, T>>> for VecDeque<T, A>
183where
184    Copied<slice::Iter<'a, T>>: Iterator<Item = T>,
185{
186    #[track_caller]
187    fn spec_extend_front(&mut self, iter: Copied<slice::Iter<'a, T>>) {
188        let slice = iter.into_inner().as_slice();
189        self.reserve(slice.len());
190        // SAFETY: `slice.len()` space was just reserved and T is Copy because Copied<slice::Iter<'a, T>> is Iterator
191        unsafe { prepend_reversed(self, slice) };
192    }
193}
194
195impl<'a, T, A: Allocator> SpecExtendFront<T, Rev<Copied<slice::Iter<'a, T>>>> for VecDeque<T, A>
196where
197    Rev<Copied<slice::Iter<'a, T>>>: Iterator<Item = T>,
198{
199    #[track_caller]
200    fn spec_extend_front(&mut self, iter: Rev<Copied<slice::Iter<'a, T>>>) {
201        let slice = iter.into_inner().into_inner().as_slice();
202        self.reserve(slice.len());
203        // SAFETY: `slice.len()` space was just reserved and T is Copy because Rev<Copied<slice::Iter<'a, T>>> is Iterator
204        unsafe { prepend(self, slice) };
205    }
206}
207
208impl<'a, T, A1: Allocator, A2: Allocator> SpecExtendFront<T, Drain<'a, T, A2>> for VecDeque<T, A1> {
209    #[track_caller]
210    fn spec_extend_front(&mut self, mut iter: Drain<'a, T, A2>) {
211        if iter.remaining == 0 {
212            return;
213        }
214
215        self.reserve(iter.remaining);
216        unsafe {
217            // SAFETY: iter.remaining != 0.
218            let (left, right) = iter.as_slices();
219            // SAFETY:
220            // - `iter.remaining` space was reserved, `iter.remaining == left.len() + right.len()`.
221            // - The elements in `left` and `right` are forgotten after these calls.
222            prepend_reversed(self, &*left);
223            prepend_reversed(self, &*right);
224        }
225
226        iter.idx += iter.remaining;
227        iter.remaining = 0;
228    }
229}
230
231impl<'a, T, A1: Allocator, A2: Allocator> SpecExtendFront<T, Rev<Drain<'a, T, A2>>>
232    for VecDeque<T, A1>
233{
234    #[track_caller]
235    fn spec_extend_front(&mut self, iter: Rev<Drain<'a, T, A2>>) {
236        let mut iter = iter.into_inner();
237
238        if iter.remaining == 0 {
239            return;
240        }
241
242        self.reserve(iter.remaining);
243        unsafe {
244            // SAFETY: iter.remaining != 0.
245            let (left, right) = iter.as_slices();
246            // SAFETY:
247            // - `iter.remaining` space was reserved, `iter.remaining == left.len() + right.len()`.
248            // - The elements in `left` and `right` are forgotten after these calls.
249            prepend(self, &*right);
250            prepend(self, &*left);
251        }
252
253        iter.idx += iter.remaining;
254        iter.remaining = 0;
255    }
256}
257
258/// Prepends elements of `slice` to `deque` using a copy.
259///
260/// # Safety
261///
262/// - `deque` must have space for `slice.len()` new elements.
263/// - Elements of `slice` will be copied into the deque, make sure to forget the elements if `T` is not `Copy`.
264unsafe fn prepend<T, A: Allocator>(deque: &mut VecDeque<T, A>, slice: &[T]) {
265    unsafe {
266        deque.head = deque.wrap_sub(deque.head, slice.len());
267        deque.copy_slice(deque.head, slice);
268        deque.len += slice.len();
269    }
270}
271
272/// Prepends elements of `slice` to `deque` in reverse order using a copy.
273///
274/// # Safety
275///
276/// - `deque` must have space for `slice.len()` new elements.
277/// - Elements of `slice` will be copied into the deque, make sure to forget the elements if `T` is not `Copy`.
278unsafe fn prepend_reversed<T, A: Allocator>(deque: &mut VecDeque<T, A>, slice: &[T]) {
279    unsafe {
280        deque.head = deque.wrap_sub(deque.head, slice.len());
281        deque.copy_slice_reversed(deque.head, slice);
282        deque.len += slice.len();
283    }
284}
alloc/collections/vec_deque/spec_extend.rs

alloc/collections/vec_deque/
spec_extend.rs
