187 lines
6.2 KiB
Rust
187 lines
6.2 KiB
Rust
// SPDX-License-Identifier: Apache-2.0 OR MIT
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use crate::alloc::{Allocator, Global};
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use core::fmt;
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use core::iter::{FusedIterator, TrustedLen};
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use core::mem;
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use core::ptr::{self, NonNull};
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use core::slice::{self};
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use super::Vec;
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/// A draining iterator for `Vec<T>`.
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///
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/// This `struct` is created by [`Vec::drain`].
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/// See its documentation for more.
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///
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/// # Example
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///
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/// ```
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/// let mut v = vec![0, 1, 2];
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/// let iter: std::vec::Drain<_> = v.drain(..);
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/// ```
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#[stable(feature = "drain", since = "1.6.0")]
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pub struct Drain<
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'a,
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T: 'a,
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#[unstable(feature = "allocator_api", issue = "32838")] A: Allocator + 'a = Global,
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> {
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/// Index of tail to preserve
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pub(super) tail_start: usize,
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/// Length of tail
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pub(super) tail_len: usize,
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/// Current remaining range to remove
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pub(super) iter: slice::Iter<'a, T>,
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pub(super) vec: NonNull<Vec<T, A>>,
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}
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#[stable(feature = "collection_debug", since = "1.17.0")]
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impl<T: fmt::Debug, A: Allocator> fmt::Debug for Drain<'_, T, A> {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.debug_tuple("Drain").field(&self.iter.as_slice()).finish()
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}
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}
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impl<'a, T, A: Allocator> Drain<'a, T, A> {
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/// Returns the remaining items of this iterator as a slice.
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///
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/// # Examples
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///
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/// ```
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/// let mut vec = vec!['a', 'b', 'c'];
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/// let mut drain = vec.drain(..);
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/// assert_eq!(drain.as_slice(), &['a', 'b', 'c']);
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/// let _ = drain.next().unwrap();
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/// assert_eq!(drain.as_slice(), &['b', 'c']);
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/// ```
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#[must_use]
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#[stable(feature = "vec_drain_as_slice", since = "1.46.0")]
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pub fn as_slice(&self) -> &[T] {
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self.iter.as_slice()
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}
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/// Returns a reference to the underlying allocator.
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#[unstable(feature = "allocator_api", issue = "32838")]
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#[must_use]
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#[inline]
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pub fn allocator(&self) -> &A {
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unsafe { self.vec.as_ref().allocator() }
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}
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}
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#[stable(feature = "vec_drain_as_slice", since = "1.46.0")]
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impl<'a, T, A: Allocator> AsRef<[T]> for Drain<'a, T, A> {
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fn as_ref(&self) -> &[T] {
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self.as_slice()
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}
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}
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#[stable(feature = "drain", since = "1.6.0")]
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unsafe impl<T: Sync, A: Sync + Allocator> Sync for Drain<'_, T, A> {}
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#[stable(feature = "drain", since = "1.6.0")]
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unsafe impl<T: Send, A: Send + Allocator> Send for Drain<'_, T, A> {}
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#[stable(feature = "drain", since = "1.6.0")]
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impl<T, A: Allocator> Iterator for Drain<'_, T, A> {
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type Item = T;
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#[inline]
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fn next(&mut self) -> Option<T> {
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self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) })
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}
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fn size_hint(&self) -> (usize, Option<usize>) {
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self.iter.size_hint()
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}
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}
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#[stable(feature = "drain", since = "1.6.0")]
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impl<T, A: Allocator> DoubleEndedIterator for Drain<'_, T, A> {
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#[inline]
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fn next_back(&mut self) -> Option<T> {
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self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) })
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}
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}
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#[stable(feature = "drain", since = "1.6.0")]
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impl<T, A: Allocator> Drop for Drain<'_, T, A> {
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fn drop(&mut self) {
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/// Moves back the un-`Drain`ed elements to restore the original `Vec`.
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struct DropGuard<'r, 'a, T, A: Allocator>(&'r mut Drain<'a, T, A>);
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impl<'r, 'a, T, A: Allocator> Drop for DropGuard<'r, 'a, T, A> {
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fn drop(&mut self) {
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if self.0.tail_len > 0 {
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unsafe {
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let source_vec = self.0.vec.as_mut();
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// memmove back untouched tail, update to new length
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let start = source_vec.len();
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let tail = self.0.tail_start;
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if tail != start {
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let src = source_vec.as_ptr().add(tail);
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let dst = source_vec.as_mut_ptr().add(start);
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ptr::copy(src, dst, self.0.tail_len);
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}
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source_vec.set_len(start + self.0.tail_len);
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}
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}
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}
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}
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let iter = mem::replace(&mut self.iter, (&mut []).iter());
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let drop_len = iter.len();
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let mut vec = self.vec;
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if mem::size_of::<T>() == 0 {
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// ZSTs have no identity, so we don't need to move them around, we only need to drop the correct amount.
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// this can be achieved by manipulating the Vec length instead of moving values out from `iter`.
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unsafe {
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let vec = vec.as_mut();
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let old_len = vec.len();
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vec.set_len(old_len + drop_len + self.tail_len);
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vec.truncate(old_len + self.tail_len);
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}
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return;
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}
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// ensure elements are moved back into their appropriate places, even when drop_in_place panics
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let _guard = DropGuard(self);
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if drop_len == 0 {
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return;
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}
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// as_slice() must only be called when iter.len() is > 0 because
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// vec::Splice modifies vec::Drain fields and may grow the vec which would invalidate
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// the iterator's internal pointers. Creating a reference to deallocated memory
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// is invalid even when it is zero-length
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let drop_ptr = iter.as_slice().as_ptr();
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unsafe {
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// drop_ptr comes from a slice::Iter which only gives us a &[T] but for drop_in_place
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// a pointer with mutable provenance is necessary. Therefore we must reconstruct
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// it from the original vec but also avoid creating a &mut to the front since that could
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// invalidate raw pointers to it which some unsafe code might rely on.
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let vec_ptr = vec.as_mut().as_mut_ptr();
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let drop_offset = drop_ptr.sub_ptr(vec_ptr);
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let to_drop = ptr::slice_from_raw_parts_mut(vec_ptr.add(drop_offset), drop_len);
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ptr::drop_in_place(to_drop);
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}
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}
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}
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#[stable(feature = "drain", since = "1.6.0")]
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impl<T, A: Allocator> ExactSizeIterator for Drain<'_, T, A> {
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fn is_empty(&self) -> bool {
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self.iter.is_empty()
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}
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}
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#[unstable(feature = "trusted_len", issue = "37572")]
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unsafe impl<T, A: Allocator> TrustedLen for Drain<'_, T, A> {}
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#[stable(feature = "fused", since = "1.26.0")]
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impl<T, A: Allocator> FusedIterator for Drain<'_, T, A> {}
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