1use core::fmt;
2use core::iter::{FusedIterator, TrustedLen};
3use core::mem::{self, ManuallyDrop, SizedTypeProperties};
4use core::ptr::{self, NonNull};
5use core::slice::{self};
6
7use super::Vec;
8use crate::alloc::{Allocator, Global};
9
10#[stable(feature = "drain", since = "1.6.0")]
22pub struct Drain<
23 'a,
24 T: 'a,
25 #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator + 'a = Global,
26> {
27 pub(super) tail_start: usize,
29 pub(super) tail_len: usize,
31 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")]
37impl<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
43impl<'a, T, A: Allocator> Drain<'a, T, A> {
44 #[must_use]
56 #[stable(feature = "vec_drain_as_slice", since = "1.46.0")]
57 pub fn as_slice(&self) -> &[T] {
58 self.iter.as_slice()
59 }
60
61 #[unstable(feature = "allocator_api", issue = "32838")]
63 #[must_use]
64 #[inline]
65 pub fn allocator(&self) -> &A {
66 unsafe { self.vec.as_ref().allocator() }
67 }
68
69 #[unstable(feature = "drain_keep_rest", issue = "101122")]
89 pub fn keep_rest(self) {
90 let mut this = ManuallyDrop::new(self);
104
105 unsafe {
106 let source_vec = this.vec.as_mut();
107
108 let start = source_vec.len();
109 let tail = this.tail_start;
110
111 let unyielded_len = this.iter.len();
112 let unyielded_ptr = this.iter.as_slice().as_ptr();
113
114 if !T::IS_ZST {
116 let start_ptr = source_vec.as_mut_ptr().add(start);
117
118 if unyielded_ptr != start_ptr {
120 let src = unyielded_ptr;
121 let dst = start_ptr;
122
123 ptr::copy(src, dst, unyielded_len);
124 }
125
126 if tail != (start + unyielded_len) {
128 let src = source_vec.as_ptr().add(tail);
129 let dst = start_ptr.add(unyielded_len);
130 ptr::copy(src, dst, this.tail_len);
131 }
132 }
133
134 source_vec.set_len(start + unyielded_len + this.tail_len);
135 }
136 }
137}
138
139#[stable(feature = "vec_drain_as_slice", since = "1.46.0")]
140impl<'a, T, A: Allocator> AsRef<[T]> for Drain<'a, T, A> {
141 fn as_ref(&self) -> &[T] {
142 self.as_slice()
143 }
144}
145
146#[stable(feature = "drain", since = "1.6.0")]
147unsafe impl<T: Sync, A: Sync + Allocator> Sync for Drain<'_, T, A> {}
148#[stable(feature = "drain", since = "1.6.0")]
149unsafe impl<T: Send, A: Send + Allocator> Send for Drain<'_, T, A> {}
150
151#[stable(feature = "drain", since = "1.6.0")]
152impl<T, A: Allocator> Iterator for Drain<'_, T, A> {
153 type Item = T;
154
155 #[inline]
156 fn next(&mut self) -> Option<T> {
157 self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) })
158 }
159
160 fn size_hint(&self) -> (usize, Option<usize>) {
161 self.iter.size_hint()
162 }
163}
164
165#[stable(feature = "drain", since = "1.6.0")]
166impl<T, A: Allocator> DoubleEndedIterator for Drain<'_, T, A> {
167 #[inline]
168 fn next_back(&mut self) -> Option<T> {
169 self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) })
170 }
171}
172
173#[stable(feature = "drain", since = "1.6.0")]
174impl<T, A: Allocator> Drop for Drain<'_, T, A> {
175 fn drop(&mut self) {
176 struct DropGuard<'r, 'a, T, A: Allocator>(&'r mut Drain<'a, T, A>);
178
179 impl<'r, 'a, T, A: Allocator> Drop for DropGuard<'r, 'a, T, A> {
180 fn drop(&mut self) {
181 if self.0.tail_len > 0 {
182 unsafe {
183 let source_vec = self.0.vec.as_mut();
184 let start = source_vec.len();
186 let tail = self.0.tail_start;
187 if tail != start {
188 let src = source_vec.as_ptr().add(tail);
189 let dst = source_vec.as_mut_ptr().add(start);
190 ptr::copy(src, dst, self.0.tail_len);
191 }
192 source_vec.set_len(start + self.0.tail_len);
193 }
194 }
195 }
196 }
197
198 let iter = mem::take(&mut self.iter);
199 let drop_len = iter.len();
200
201 let mut vec = self.vec;
202
203 if T::IS_ZST {
204 unsafe {
207 let vec = vec.as_mut();
208 let old_len = vec.len();
209 vec.set_len(old_len + drop_len + self.tail_len);
210 vec.truncate(old_len + self.tail_len);
211 }
212
213 return;
214 }
215
216 let _guard = DropGuard(self);
218
219 if drop_len == 0 {
220 return;
221 }
222
223 let drop_ptr = iter.as_slice().as_ptr();
228
229 unsafe {
230 let vec_ptr = vec.as_mut().as_mut_ptr();
235 let drop_offset = drop_ptr.offset_from_unsigned(vec_ptr);
236 let to_drop = ptr::slice_from_raw_parts_mut(vec_ptr.add(drop_offset), drop_len);
237 ptr::drop_in_place(to_drop);
238 }
239 }
240}
241
242#[stable(feature = "drain", since = "1.6.0")]
243impl<T, A: Allocator> ExactSizeIterator for Drain<'_, T, A> {
244 fn is_empty(&self) -> bool {
245 self.iter.is_empty()
246 }
247}
248
249#[unstable(feature = "trusted_len", issue = "37572")]
250unsafe impl<T, A: Allocator> TrustedLen for Drain<'_, T, A> {}
251
252#[stable(feature = "fused", since = "1.26.0")]
253impl<T, A: Allocator> FusedIterator for Drain<'_, T, A> {}