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// SPDX-License-Identifier: Apache-2.0 OR MIT
use crate::alloc::{Allocator, Global};
use core::ptr;
use core::slice;
use super::Vec;
/// An iterator which uses a closure to determine if an element should be removed.
///
/// This struct is created by [`Vec::extract_if`].
/// See its documentation for more.
///
/// # Example
///
/// ```
/// #![feature(extract_if)]
///
/// let mut v = vec![0, 1, 2];
/// let iter: std::vec::ExtractIf<'_, _, _> = v.extract_if(|x| *x % 2 == 0);
/// ```
#[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
#[derive(Debug)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
pub struct ExtractIf<
'a,
T,
F,
#[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
> where
F: FnMut(&mut T) -> bool,
{
pub(super) vec: &'a mut Vec<T, A>,
/// The index of the item that will be inspected by the next call to `next`.
pub(super) idx: usize,
/// The number of items that have been drained (removed) thus far.
pub(super) del: usize,
/// The original length of `vec` prior to draining.
pub(super) old_len: usize,
/// The filter test predicate.
pub(super) pred: F,
}
impl<T, F, A: Allocator> ExtractIf<'_, T, F, A>
where
F: FnMut(&mut T) -> bool,
{
/// Returns a reference to the underlying allocator.
#[unstable(feature = "allocator_api", issue = "32838")]
#[inline]
pub fn allocator(&self) -> &A {
self.vec.allocator()
}
}
#[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
impl<T, F, A: Allocator> Iterator for ExtractIf<'_, T, F, A>
where
F: FnMut(&mut T) -> bool,
{
type Item = T;
fn next(&mut self) -> Option<T> {
unsafe {
while self.idx < self.old_len {
let i = self.idx;
let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
let drained = (self.pred)(&mut v[i]);
// Update the index *after* the predicate is called. If the index
// is updated prior and the predicate panics, the element at this
// index would be leaked.
self.idx += 1;
if drained {
self.del += 1;
return Some(ptr::read(&v[i]));
} else if self.del > 0 {
let del = self.del;
let src: *const T = &v[i];
let dst: *mut T = &mut v[i - del];
ptr::copy_nonoverlapping(src, dst, 1);
}
}
None
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
(0, Some(self.old_len - self.idx))
}
}
#[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
impl<T, F, A: Allocator> Drop for ExtractIf<'_, T, F, A>
where
F: FnMut(&mut T) -> bool,
{
fn drop(&mut self) {
unsafe {
if self.idx < self.old_len && self.del > 0 {
// This is a pretty messed up state, and there isn't really an
// obviously right thing to do. We don't want to keep trying
// to execute `pred`, so we just backshift all the unprocessed
// elements and tell the vec that they still exist. The backshift
// is required to prevent a double-drop of the last successfully
// drained item prior to a panic in the predicate.
let ptr = self.vec.as_mut_ptr();
let src = ptr.add(self.idx);
let dst = src.sub(self.del);
let tail_len = self.old_len - self.idx;
src.copy_to(dst, tail_len);
}
self.vec.set_len(self.old_len - self.del);
}
}
}
|
