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5869c6ff XL |
1 | use crate::alloc::{Allocator, Global}; |
2 | use core::fmt; | |
3 | use core::iter::{FusedIterator, TrustedLen}; | |
4 | use core::mem::{self}; | |
5 | use core::ptr::{self, NonNull}; | |
6 | use core::slice::{self}; | |
7 | ||
8 | use super::Vec; | |
9 | ||
10 | /// A draining iterator for `Vec<T>`. | |
11 | /// | |
12 | /// This `struct` is created by [`Vec::drain`]. | |
13 | /// See its documentation for more. | |
14 | /// | |
15 | /// # Example | |
16 | /// | |
17 | /// ``` | |
18 | /// let mut v = vec![0, 1, 2]; | |
19 | /// let iter: std::vec::Drain<_> = v.drain(..); | |
20 | /// ``` | |
21 | #[stable(feature = "drain", since = "1.6.0")] | |
22 | pub struct Drain< | |
23 | 'a, | |
24 | T: 'a, | |
25 | #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator + 'a = Global, | |
26 | > { | |
27 | /// Index of tail to preserve | |
28 | pub(super) tail_start: usize, | |
29 | /// Length of tail | |
30 | pub(super) tail_len: usize, | |
31 | /// Current remaining range to remove | |
32 | pub(super) iter: slice::Iter<'a, T>, | |
33 | pub(super) vec: NonNull<Vec<T, A>>, | |
34 | } | |
35 | ||
36 | #[stable(feature = "collection_debug", since = "1.17.0")] | |
37 | impl<T: fmt::Debug, A: Allocator> fmt::Debug for Drain<'_, T, A> { | |
38 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { | |
39 | f.debug_tuple("Drain").field(&self.iter.as_slice()).finish() | |
40 | } | |
41 | } | |
42 | ||
43 | impl<'a, T, A: Allocator> Drain<'a, T, A> { | |
44 | /// Returns the remaining items of this iterator as a slice. | |
45 | /// | |
46 | /// # Examples | |
47 | /// | |
48 | /// ``` | |
49 | /// let mut vec = vec!['a', 'b', 'c']; | |
50 | /// let mut drain = vec.drain(..); | |
51 | /// assert_eq!(drain.as_slice(), &['a', 'b', 'c']); | |
52 | /// let _ = drain.next().unwrap(); | |
53 | /// assert_eq!(drain.as_slice(), &['b', 'c']); | |
54 | /// ``` | |
55 | #[stable(feature = "vec_drain_as_slice", since = "1.46.0")] | |
56 | pub fn as_slice(&self) -> &[T] { | |
57 | self.iter.as_slice() | |
58 | } | |
59 | ||
60 | /// Returns a reference to the underlying allocator. | |
61 | #[unstable(feature = "allocator_api", issue = "32838")] | |
62 | #[inline] | |
63 | pub fn allocator(&self) -> &A { | |
64 | unsafe { self.vec.as_ref().allocator() } | |
65 | } | |
66 | } | |
67 | ||
68 | #[stable(feature = "vec_drain_as_slice", since = "1.46.0")] | |
69 | impl<'a, T, A: Allocator> AsRef<[T]> for Drain<'a, T, A> { | |
70 | fn as_ref(&self) -> &[T] { | |
71 | self.as_slice() | |
72 | } | |
73 | } | |
74 | ||
75 | #[stable(feature = "drain", since = "1.6.0")] | |
76 | unsafe impl<T: Sync, A: Sync + Allocator> Sync for Drain<'_, T, A> {} | |
77 | #[stable(feature = "drain", since = "1.6.0")] | |
78 | unsafe impl<T: Send, A: Send + Allocator> Send for Drain<'_, T, A> {} | |
79 | ||
80 | #[stable(feature = "drain", since = "1.6.0")] | |
81 | impl<T, A: Allocator> Iterator for Drain<'_, T, A> { | |
82 | type Item = T; | |
83 | ||
84 | #[inline] | |
85 | fn next(&mut self) -> Option<T> { | |
86 | self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) }) | |
87 | } | |
88 | ||
89 | fn size_hint(&self) -> (usize, Option<usize>) { | |
90 | self.iter.size_hint() | |
91 | } | |
92 | } | |
93 | ||
94 | #[stable(feature = "drain", since = "1.6.0")] | |
95 | impl<T, A: Allocator> DoubleEndedIterator for Drain<'_, T, A> { | |
96 | #[inline] | |
97 | fn next_back(&mut self) -> Option<T> { | |
98 | self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) }) | |
99 | } | |
100 | } | |
101 | ||
102 | #[stable(feature = "drain", since = "1.6.0")] | |
103 | impl<T, A: Allocator> Drop for Drain<'_, T, A> { | |
104 | fn drop(&mut self) { | |
105 | /// Continues dropping the remaining elements in the `Drain`, then moves back the | |
106 | /// un-`Drain`ed elements to restore the original `Vec`. | |
107 | struct DropGuard<'r, 'a, T, A: Allocator>(&'r mut Drain<'a, T, A>); | |
108 | ||
109 | impl<'r, 'a, T, A: Allocator> Drop for DropGuard<'r, 'a, T, A> { | |
110 | fn drop(&mut self) { | |
111 | // Continue the same loop we have below. If the loop already finished, this does | |
112 | // nothing. | |
113 | self.0.for_each(drop); | |
114 | ||
115 | if self.0.tail_len > 0 { | |
116 | unsafe { | |
117 | let source_vec = self.0.vec.as_mut(); | |
118 | // memmove back untouched tail, update to new length | |
119 | let start = source_vec.len(); | |
120 | let tail = self.0.tail_start; | |
121 | if tail != start { | |
122 | let src = source_vec.as_ptr().add(tail); | |
123 | let dst = source_vec.as_mut_ptr().add(start); | |
124 | ptr::copy(src, dst, self.0.tail_len); | |
125 | } | |
126 | source_vec.set_len(start + self.0.tail_len); | |
127 | } | |
128 | } | |
129 | } | |
130 | } | |
131 | ||
132 | // exhaust self first | |
133 | while let Some(item) = self.next() { | |
134 | let guard = DropGuard(self); | |
135 | drop(item); | |
136 | mem::forget(guard); | |
137 | } | |
138 | ||
139 | // Drop a `DropGuard` to move back the non-drained tail of `self`. | |
140 | DropGuard(self); | |
141 | } | |
142 | } | |
143 | ||
144 | #[stable(feature = "drain", since = "1.6.0")] | |
145 | impl<T, A: Allocator> ExactSizeIterator for Drain<'_, T, A> { | |
146 | fn is_empty(&self) -> bool { | |
147 | self.iter.is_empty() | |
148 | } | |
149 | } | |
150 | ||
151 | #[unstable(feature = "trusted_len", issue = "37572")] | |
152 | unsafe impl<T, A: Allocator> TrustedLen for Drain<'_, T, A> {} | |
153 | ||
154 | #[stable(feature = "fused", since = "1.26.0")] | |
155 | impl<T, A: Allocator> FusedIterator for Drain<'_, T, A> {} |