alloc/vec/
extract_if.rs

1use core::ops::{Range, RangeBounds};
2use core::{fmt, ptr, slice};
3
4use super::Vec;
5use crate::alloc::{Allocator, Global};
6
7/// An iterator which uses a closure to determine if an element should be removed.
8///
9/// This struct is created by [`Vec::extract_if`].
10/// See its documentation for more.
11///
12/// # Example
13///
14/// ```
15/// let mut v = vec![0, 1, 2];
16/// let iter: std::vec::ExtractIf<'_, _, _> = v.extract_if(.., |x| *x % 2 == 0);
17/// ```
18#[stable(feature = "extract_if", since = "1.87.0")]
19#[must_use = "iterators are lazy and do nothing unless consumed"]
20pub struct ExtractIf<
21    'a,
22    T,
23    F,
24    #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
25> {
26    vec: &'a mut Vec<T, A>,
27    /// The index of the item that will be inspected by the next call to `next`.
28    idx: usize,
29    /// Elements at and beyond this point will be retained. Must be equal or smaller than `old_len`.
30    end: usize,
31    /// The number of items that have been drained (removed) thus far.
32    del: usize,
33    /// The original length of `vec` prior to draining.
34    old_len: usize,
35    /// The filter test predicate.
36    pred: F,
37}
38
39impl<'a, T, F, A: Allocator> ExtractIf<'a, T, F, A> {
40    pub(super) fn new<R: RangeBounds<usize>>(vec: &'a mut Vec<T, A>, pred: F, range: R) -> Self {
41        let old_len = vec.len();
42        let Range { start, end } = slice::range(range, ..old_len);
43
44        // Guard against the vec getting leaked (leak amplification)
45        unsafe {
46            vec.set_len(0);
47        }
48        ExtractIf { vec, idx: start, del: 0, end, old_len, pred }
49    }
50
51    /// Returns a reference to the underlying allocator.
52    #[unstable(feature = "allocator_api", issue = "32838")]
53    #[inline]
54    pub fn allocator(&self) -> &A {
55        self.vec.allocator()
56    }
57}
58
59#[stable(feature = "extract_if", since = "1.87.0")]
60impl<T, F, A: Allocator> Iterator for ExtractIf<'_, T, F, A>
61where
62    F: FnMut(&mut T) -> bool,
63{
64    type Item = T;
65
66    fn next(&mut self) -> Option<T> {
67        unsafe {
68            while self.idx < self.end {
69                let i = self.idx;
70                let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
71                let drained = (self.pred)(&mut v[i]);
72                // Update the index *after* the predicate is called. If the index
73                // is updated prior and the predicate panics, the element at this
74                // index would be leaked.
75                self.idx += 1;
76                if drained {
77                    self.del += 1;
78                    return Some(ptr::read(&v[i]));
79                } else if self.del > 0 {
80                    let del = self.del;
81                    let src: *const T = &v[i];
82                    let dst: *mut T = &mut v[i - del];
83                    ptr::copy_nonoverlapping(src, dst, 1);
84                }
85            }
86            None
87        }
88    }
89
90    fn size_hint(&self) -> (usize, Option<usize>) {
91        (0, Some(self.end - self.idx))
92    }
93}
94
95#[stable(feature = "extract_if", since = "1.87.0")]
96impl<T, F, A: Allocator> Drop for ExtractIf<'_, T, F, A> {
97    fn drop(&mut self) {
98        unsafe {
99            if self.idx < self.old_len && self.del > 0 {
100                let ptr = self.vec.as_mut_ptr();
101                let src = ptr.add(self.idx);
102                let dst = src.sub(self.del);
103                let tail_len = self.old_len - self.idx;
104                src.copy_to(dst, tail_len);
105            }
106            self.vec.set_len(self.old_len - self.del);
107        }
108    }
109}
110
111#[stable(feature = "extract_if", since = "1.87.0")]
112impl<T, F, A> fmt::Debug for ExtractIf<'_, T, F, A>
113where
114    T: fmt::Debug,
115    A: Allocator,
116{
117    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
118        let peek = if self.idx < self.end { self.vec.get(self.idx) } else { None };
119        f.debug_struct("ExtractIf").field("peek", &peek).finish_non_exhaustive()
120    }
121}
alloc/vec/extract_if.rs

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alloc/vec/
extract_if.rs
