alloc/collections/vec_deque/
spec_extend.rs

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1use core::iter::TrustedLen;
2use core::slice;
3
4use super::VecDeque;
5use crate::alloc::Allocator;
6use crate::vec;
7
8// Specialization trait used for VecDeque::extend
9pub(super) trait SpecExtend<T, I> {
10    #[track_caller]
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    #[track_caller]
19    default fn spec_extend(&mut self, mut iter: I) {
20        // This function should be the moral equivalent of:
21        //
22        // for item in iter {
23        //     self.push_back(item);
24        // }
25
26        while let Some(element) = iter.next() {
27            let (lower, _) = iter.size_hint();
28            self.reserve(lower.saturating_add(1));
29
30            // SAFETY: We just reserved space for at least one element.
31            unsafe { self.push_unchecked(element) };
32
33            // Inner loop to avoid repeatedly calling `reserve`.
34            while self.len < self.capacity() {
35                let Some(element) = iter.next() else {
36                    return;
37                };
38                // SAFETY: The loop condition guarantees that `self.len() < self.capacity()`.
39                unsafe { self.push_unchecked(element) };
40            }
41        }
42    }
43}
44
45impl<T, I, A: Allocator> SpecExtend<T, I> for VecDeque<T, A>
46where
47    I: TrustedLen<Item = T>,
48{
49    #[track_caller]
50    default fn spec_extend(&mut self, iter: I) {
51        // This is the case for a TrustedLen iterator.
52        let (low, high) = iter.size_hint();
53        if let Some(additional) = high {
54            debug_assert_eq!(
55                low,
56                additional,
57                "TrustedLen iterator's size hint is not exact: {:?}",
58                (low, high)
59            );
60            self.reserve(additional);
61
62            let written = unsafe {
63                self.write_iter_wrapping(self.to_physical_idx(self.len), iter, additional)
64            };
65
66            debug_assert_eq!(
67                additional, written,
68                "The number of items written to VecDeque doesn't match the TrustedLen size hint"
69            );
70        } else {
71            // Per TrustedLen contract a `None` upper bound means that the iterator length
72            // truly exceeds usize::MAX, which would eventually lead to a capacity overflow anyway.
73            // Since the other branch already panics eagerly (via `reserve()`) we do the same here.
74            // This avoids additional codegen for a fallback code path which would eventually
75            // panic anyway.
76            panic!("capacity overflow");
77        }
78    }
79}
80
81impl<T, A: Allocator> SpecExtend<T, vec::IntoIter<T>> for VecDeque<T, A> {
82    #[track_caller]
83    fn spec_extend(&mut self, mut iterator: vec::IntoIter<T>) {
84        let slice = iterator.as_slice();
85        self.reserve(slice.len());
86
87        unsafe {
88            self.copy_slice(self.to_physical_idx(self.len), slice);
89            self.len += slice.len();
90        }
91        iterator.forget_remaining_elements();
92    }
93}
94
95impl<'a, T: 'a, I, A: Allocator> SpecExtend<&'a T, I> for VecDeque<T, A>
96where
97    I: Iterator<Item = &'a T>,
98    T: Copy,
99{
100    #[track_caller]
101    default fn spec_extend(&mut self, iterator: I) {
102        self.spec_extend(iterator.copied())
103    }
104}
105
106impl<'a, T: 'a, A: Allocator> SpecExtend<&'a T, slice::Iter<'a, T>> for VecDeque<T, A>
107where
108    T: Copy,
109{
110    #[track_caller]
111    fn spec_extend(&mut self, iterator: slice::Iter<'a, T>) {
112        let slice = iterator.as_slice();
113        self.reserve(slice.len());
114
115        unsafe {
116            self.copy_slice(self.to_physical_idx(self.len), slice);
117            self.len += slice.len();
118        }
119    }
120}
alloc/collections/vec_deque/spec_extend.rs

alloc/collections/vec_deque/
spec_extend.rs
