alloc/vec/
extract_if.rs

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

alloc/vec/
extract_if.rs
