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| 1 | +use crate::alloc::{Allocator, Global}; |
| 2 | +use core::iter::{ |
| 3 | + FusedIterator, TrustedLen, |
| 4 | +}; |
| 5 | +use core::mem::{self}; |
| 6 | +use core::ptr::{self, NonNull}; |
| 7 | +use core::slice::{self}; |
| 8 | +use core::fmt; |
| 9 | + |
| 10 | +use super::{Vec}; |
| 11 | + |
| 12 | +/// A draining iterator for `Vec<T>`. |
| 13 | +/// |
| 14 | +/// This `struct` is created by [`Vec::drain`]. |
| 15 | +/// See its documentation for more. |
| 16 | +/// |
| 17 | +/// # Example |
| 18 | +/// |
| 19 | +/// ``` |
| 20 | +/// let mut v = vec![0, 1, 2]; |
| 21 | +/// let iter: std::vec::Drain<_> = v.drain(..); |
| 22 | +/// ``` |
| 23 | +#[stable(feature = "drain", since = "1.6.0")] |
| 24 | +pub struct Drain< |
| 25 | + 'a, |
| 26 | + T: 'a, |
| 27 | + #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator + 'a = Global, |
| 28 | +> { |
| 29 | + /// Index of tail to preserve |
| 30 | + pub(super) tail_start: usize, |
| 31 | + /// Length of tail |
| 32 | + pub(super) tail_len: usize, |
| 33 | + /// Current remaining range to remove |
| 34 | + pub(super) iter: slice::Iter<'a, T>, |
| 35 | + pub(super) vec: NonNull<Vec<T, A>>, |
| 36 | +} |
| 37 | + |
| 38 | +#[stable(feature = "collection_debug", since = "1.17.0")] |
| 39 | +impl<T: fmt::Debug, A: Allocator> fmt::Debug for Drain<'_, T, A> { |
| 40 | + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| 41 | + f.debug_tuple("Drain").field(&self.iter.as_slice()).finish() |
| 42 | + } |
| 43 | +} |
| 44 | + |
| 45 | +impl<'a, T, A: Allocator> Drain<'a, T, A> { |
| 46 | + /// Returns the remaining items of this iterator as a slice. |
| 47 | + /// |
| 48 | + /// # Examples |
| 49 | + /// |
| 50 | + /// ``` |
| 51 | + /// let mut vec = vec!['a', 'b', 'c']; |
| 52 | + /// let mut drain = vec.drain(..); |
| 53 | + /// assert_eq!(drain.as_slice(), &['a', 'b', 'c']); |
| 54 | + /// let _ = drain.next().unwrap(); |
| 55 | + /// assert_eq!(drain.as_slice(), &['b', 'c']); |
| 56 | + /// ``` |
| 57 | + #[stable(feature = "vec_drain_as_slice", since = "1.46.0")] |
| 58 | + pub fn as_slice(&self) -> &[T] { |
| 59 | + self.iter.as_slice() |
| 60 | + } |
| 61 | + |
| 62 | + /// Returns a reference to the underlying allocator. |
| 63 | + #[unstable(feature = "allocator_api", issue = "32838")] |
| 64 | + #[inline] |
| 65 | + pub fn allocator(&self) -> &A { |
| 66 | + unsafe { self.vec.as_ref().allocator() } |
| 67 | + } |
| 68 | +} |
| 69 | + |
| 70 | +#[stable(feature = "vec_drain_as_slice", since = "1.46.0")] |
| 71 | +impl<'a, T, A: Allocator> AsRef<[T]> for Drain<'a, T, A> { |
| 72 | + fn as_ref(&self) -> &[T] { |
| 73 | + self.as_slice() |
| 74 | + } |
| 75 | +} |
| 76 | + |
| 77 | +#[stable(feature = "drain", since = "1.6.0")] |
| 78 | +unsafe impl<T: Sync, A: Sync + Allocator> Sync for Drain<'_, T, A> {} |
| 79 | +#[stable(feature = "drain", since = "1.6.0")] |
| 80 | +unsafe impl<T: Send, A: Send + Allocator> Send for Drain<'_, T, A> {} |
| 81 | + |
| 82 | +#[stable(feature = "drain", since = "1.6.0")] |
| 83 | +impl<T, A: Allocator> Iterator for Drain<'_, T, A> { |
| 84 | + type Item = T; |
| 85 | + |
| 86 | + #[inline] |
| 87 | + fn next(&mut self) -> Option<T> { |
| 88 | + self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) }) |
| 89 | + } |
| 90 | + |
| 91 | + fn size_hint(&self) -> (usize, Option<usize>) { |
| 92 | + self.iter.size_hint() |
| 93 | + } |
| 94 | +} |
| 95 | + |
| 96 | +#[stable(feature = "drain", since = "1.6.0")] |
| 97 | +impl<T, A: Allocator> DoubleEndedIterator for Drain<'_, T, A> { |
| 98 | + #[inline] |
| 99 | + fn next_back(&mut self) -> Option<T> { |
| 100 | + self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) }) |
| 101 | + } |
| 102 | +} |
| 103 | + |
| 104 | +#[stable(feature = "drain", since = "1.6.0")] |
| 105 | +impl<T, A: Allocator> Drop for Drain<'_, T, A> { |
| 106 | + fn drop(&mut self) { |
| 107 | + /// Continues dropping the remaining elements in the `Drain`, then moves back the |
| 108 | + /// un-`Drain`ed elements to restore the original `Vec`. |
| 109 | + struct DropGuard<'r, 'a, T, A: Allocator>(&'r mut Drain<'a, T, A>); |
| 110 | + |
| 111 | + impl<'r, 'a, T, A: Allocator> Drop for DropGuard<'r, 'a, T, A> { |
| 112 | + fn drop(&mut self) { |
| 113 | + // Continue the same loop we have below. If the loop already finished, this does |
| 114 | + // nothing. |
| 115 | + self.0.for_each(drop); |
| 116 | + |
| 117 | + if self.0.tail_len > 0 { |
| 118 | + unsafe { |
| 119 | + let source_vec = self.0.vec.as_mut(); |
| 120 | + // memmove back untouched tail, update to new length |
| 121 | + let start = source_vec.len(); |
| 122 | + let tail = self.0.tail_start; |
| 123 | + if tail != start { |
| 124 | + let src = source_vec.as_ptr().add(tail); |
| 125 | + let dst = source_vec.as_mut_ptr().add(start); |
| 126 | + ptr::copy(src, dst, self.0.tail_len); |
| 127 | + } |
| 128 | + source_vec.set_len(start + self.0.tail_len); |
| 129 | + } |
| 130 | + } |
| 131 | + } |
| 132 | + } |
| 133 | + |
| 134 | + // exhaust self first |
| 135 | + while let Some(item) = self.next() { |
| 136 | + let guard = DropGuard(self); |
| 137 | + drop(item); |
| 138 | + mem::forget(guard); |
| 139 | + } |
| 140 | + |
| 141 | + // Drop a `DropGuard` to move back the non-drained tail of `self`. |
| 142 | + DropGuard(self); |
| 143 | + } |
| 144 | +} |
| 145 | + |
| 146 | +#[stable(feature = "drain", since = "1.6.0")] |
| 147 | +impl<T, A: Allocator> ExactSizeIterator for Drain<'_, T, A> { |
| 148 | + fn is_empty(&self) -> bool { |
| 149 | + self.iter.is_empty() |
| 150 | + } |
| 151 | +} |
| 152 | + |
| 153 | +#[unstable(feature = "trusted_len", issue = "37572")] |
| 154 | +unsafe impl<T, A: Allocator> TrustedLen for Drain<'_, T, A> {} |
| 155 | + |
| 156 | +#[stable(feature = "fused", since = "1.26.0")] |
| 157 | +impl<T, A: Allocator> FusedIterator for Drain<'_, T, A> {} |
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