refactor: moving DrainFilter into drain_filter.rs
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143
library/alloc/src/vec/drain_filter.rs
Normal file
143
library/alloc/src/vec/drain_filter.rs
Normal file
@ -0,0 +1,143 @@
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use core::ptr::{self};
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use core::slice::{self};
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use crate::alloc::{Allocator, Global};
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use super::{Vec};
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/// An iterator which uses a closure to determine if an element should be removed.
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///
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/// This struct is created by [`Vec::drain_filter`].
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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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/// #![feature(drain_filter)]
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///
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/// let mut v = vec![0, 1, 2];
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/// let iter: std::vec::DrainFilter<_, _> = v.drain_filter(|x| *x % 2 == 0);
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/// ```
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#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
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#[derive(Debug)]
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pub struct DrainFilter<
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'a,
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T,
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F,
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#[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
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> where
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F: FnMut(&mut T) -> bool,
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{
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pub(super) vec: &'a mut Vec<T, A>,
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/// The index of the item that will be inspected by the next call to `next`.
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pub(super) idx: usize,
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/// The number of items that have been drained (removed) thus far.
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pub(super) del: usize,
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/// The original length of `vec` prior to draining.
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pub(super) old_len: usize,
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/// The filter test predicate.
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pub(super) pred: F,
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/// A flag that indicates a panic has occurred in the filter test predicate.
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/// This is used as a hint in the drop implementation to prevent consumption
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/// of the remainder of the `DrainFilter`. Any unprocessed items will be
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/// backshifted in the `vec`, but no further items will be dropped or
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/// tested by the filter predicate.
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pub(super) panic_flag: bool,
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}
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impl<T, F, A: Allocator> DrainFilter<'_, T, F, A>
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where
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F: FnMut(&mut T) -> bool,
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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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#[inline]
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pub fn allocator(&self) -> &A {
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self.vec.allocator()
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}
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}
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#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
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impl<T, F, A: Allocator> Iterator for DrainFilter<'_, T, F, A>
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where
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F: FnMut(&mut T) -> bool,
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{
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type Item = T;
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fn next(&mut self) -> Option<T> {
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unsafe {
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while self.idx < self.old_len {
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let i = self.idx;
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let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
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self.panic_flag = true;
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let drained = (self.pred)(&mut v[i]);
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self.panic_flag = false;
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// Update the index *after* the predicate is called. If the index
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// is updated prior and the predicate panics, the element at this
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// index would be leaked.
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self.idx += 1;
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if drained {
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self.del += 1;
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return Some(ptr::read(&v[i]));
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} else if self.del > 0 {
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let del = self.del;
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let src: *const T = &v[i];
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let dst: *mut T = &mut v[i - del];
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ptr::copy_nonoverlapping(src, dst, 1);
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}
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}
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None
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}
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}
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fn size_hint(&self) -> (usize, Option<usize>) {
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(0, Some(self.old_len - self.idx))
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}
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}
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#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
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impl<T, F, A: Allocator> Drop for DrainFilter<'_, T, F, A>
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where
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F: FnMut(&mut T) -> bool,
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{
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fn drop(&mut self) {
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struct BackshiftOnDrop<'a, 'b, T, F, A: Allocator>
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where
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F: FnMut(&mut T) -> bool,
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{
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drain: &'b mut DrainFilter<'a, T, F, A>,
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}
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impl<'a, 'b, T, F, A: Allocator> Drop for BackshiftOnDrop<'a, 'b, T, F, A>
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where
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F: FnMut(&mut T) -> bool,
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{
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fn drop(&mut self) {
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unsafe {
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if self.drain.idx < self.drain.old_len && self.drain.del > 0 {
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// This is a pretty messed up state, and there isn't really an
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// obviously right thing to do. We don't want to keep trying
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// to execute `pred`, so we just backshift all the unprocessed
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// elements and tell the vec that they still exist. The backshift
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// is required to prevent a double-drop of the last successfully
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// drained item prior to a panic in the predicate.
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let ptr = self.drain.vec.as_mut_ptr();
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let src = ptr.add(self.drain.idx);
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let dst = src.sub(self.drain.del);
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let tail_len = self.drain.old_len - self.drain.idx;
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src.copy_to(dst, tail_len);
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}
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self.drain.vec.set_len(self.drain.old_len - self.drain.del);
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}
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}
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}
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let backshift = BackshiftOnDrop { drain: self };
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// Attempt to consume any remaining elements if the filter predicate
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// has not yet panicked. We'll backshift any remaining elements
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// whether we've already panicked or if the consumption here panics.
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if !backshift.drain.panic_flag {
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backshift.drain.for_each(drop);
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}
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}
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}
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@ -74,6 +74,11 @@ use crate::boxed::Box;
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use crate::collections::TryReserveError;
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use crate::raw_vec::RawVec;
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#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
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pub use self::drain_filter::DrainFilter;
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mod drain_filter;
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/// A contiguous growable array type, written `Vec<T>` but pronounced 'vector'.
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///
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/// # Examples
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@ -3585,141 +3590,3 @@ impl<T, A: Allocator> Drain<'_, T, A> {
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self.tail_start = new_tail_start;
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}
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}
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/// An iterator which uses a closure to determine if an element should be removed.
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///
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/// This struct is created by [`Vec::drain_filter`].
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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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/// #![feature(drain_filter)]
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///
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/// let mut v = vec![0, 1, 2];
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/// let iter: std::vec::DrainFilter<_, _> = v.drain_filter(|x| *x % 2 == 0);
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/// ```
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#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
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#[derive(Debug)]
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pub struct DrainFilter<
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'a,
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T,
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F,
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#[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
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> where
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F: FnMut(&mut T) -> bool,
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{
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vec: &'a mut Vec<T, A>,
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/// The index of the item that will be inspected by the next call to `next`.
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idx: usize,
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/// The number of items that have been drained (removed) thus far.
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del: usize,
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/// The original length of `vec` prior to draining.
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old_len: usize,
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/// The filter test predicate.
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pred: F,
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/// A flag that indicates a panic has occurred in the filter test predicate.
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/// This is used as a hint in the drop implementation to prevent consumption
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/// of the remainder of the `DrainFilter`. Any unprocessed items will be
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/// backshifted in the `vec`, but no further items will be dropped or
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/// tested by the filter predicate.
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panic_flag: bool,
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}
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impl<T, F, A: Allocator> DrainFilter<'_, T, F, A>
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where
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F: FnMut(&mut T) -> bool,
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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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#[inline]
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pub fn allocator(&self) -> &A {
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self.vec.allocator()
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}
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}
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#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
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impl<T, F, A: Allocator> Iterator for DrainFilter<'_, T, F, A>
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where
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F: FnMut(&mut T) -> bool,
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{
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type Item = T;
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fn next(&mut self) -> Option<T> {
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unsafe {
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while self.idx < self.old_len {
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let i = self.idx;
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let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
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self.panic_flag = true;
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let drained = (self.pred)(&mut v[i]);
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self.panic_flag = false;
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// Update the index *after* the predicate is called. If the index
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// is updated prior and the predicate panics, the element at this
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// index would be leaked.
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self.idx += 1;
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if drained {
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self.del += 1;
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return Some(ptr::read(&v[i]));
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} else if self.del > 0 {
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let del = self.del;
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let src: *const T = &v[i];
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let dst: *mut T = &mut v[i - del];
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ptr::copy_nonoverlapping(src, dst, 1);
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}
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}
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None
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}
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}
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fn size_hint(&self) -> (usize, Option<usize>) {
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(0, Some(self.old_len - self.idx))
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}
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}
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#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
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impl<T, F, A: Allocator> Drop for DrainFilter<'_, T, F, A>
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where
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F: FnMut(&mut T) -> bool,
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{
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fn drop(&mut self) {
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struct BackshiftOnDrop<'a, 'b, T, F, A: Allocator>
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where
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F: FnMut(&mut T) -> bool,
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{
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drain: &'b mut DrainFilter<'a, T, F, A>,
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}
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impl<'a, 'b, T, F, A: Allocator> Drop for BackshiftOnDrop<'a, 'b, T, F, A>
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where
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F: FnMut(&mut T) -> bool,
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{
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fn drop(&mut self) {
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unsafe {
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if self.drain.idx < self.drain.old_len && self.drain.del > 0 {
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// This is a pretty messed up state, and there isn't really an
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// obviously right thing to do. We don't want to keep trying
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// to execute `pred`, so we just backshift all the unprocessed
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// elements and tell the vec that they still exist. The backshift
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// is required to prevent a double-drop of the last successfully
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// drained item prior to a panic in the predicate.
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let ptr = self.drain.vec.as_mut_ptr();
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let src = ptr.add(self.drain.idx);
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let dst = src.sub(self.drain.del);
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let tail_len = self.drain.old_len - self.drain.idx;
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src.copy_to(dst, tail_len);
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}
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self.drain.vec.set_len(self.drain.old_len - self.drain.del);
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}
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}
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}
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let backshift = BackshiftOnDrop { drain: self };
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// Attempt to consume any remaining elements if the filter predicate
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// has not yet panicked. We'll backshift any remaining elements
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// whether we've already panicked or if the consumption here panics.
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if !backshift.drain.panic_flag {
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backshift.drain.for_each(drop);
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}
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}
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}
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