1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
|
use core::ops::{Range, RangeBounds};
use core::{fmt, ptr, slice};
use super::Vec;
use crate::alloc::{Allocator, Global};
/// 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
///
/// ```
/// let mut v = vec![0, 1, 2];
/// let iter: std::vec::ExtractIf<'_, _, _> = v.extract_if(.., |x| *x % 2 == 0);
/// ```
#[stable(feature = "extract_if", since = "1.87.0")]
#[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,
> {
vec: &'a mut Vec<T, A>,
/// The index of the item that will be inspected by the next call to `next`.
idx: usize,
/// Elements at and beyond this point will be retained. Must be equal or smaller than `old_len`.
end: usize,
/// The number of items that have been drained (removed) thus far.
del: usize,
/// The original length of `vec` prior to draining.
old_len: usize,
/// The filter test predicate.
pred: F,
}
impl<'a, T, F, A: Allocator> ExtractIf<'a, T, F, A> {
pub(super) fn new<R: RangeBounds<usize>>(vec: &'a mut Vec<T, A>, pred: F, range: R) -> Self {
let old_len = vec.len();
let Range { start, end } = slice::range(range, ..old_len);
// Guard against the vec getting leaked (leak amplification)
unsafe {
vec.set_len(0);
}
ExtractIf { vec, idx: start, del: 0, end, old_len, pred }
}
/// Returns a reference to the underlying allocator.
#[unstable(feature = "allocator_api", issue = "32838")]
#[inline]
pub fn allocator(&self) -> &A {
self.vec.allocator()
}
}
#[stable(feature = "extract_if", since = "1.87.0")]
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> {
while self.idx < self.end {
let i = self.idx;
// SAFETY:
// We know that `i < self.end` from the if guard and that `self.end <= self.old_len` from
// the validity of `Self`. Therefore `i` points to an element within `vec`.
//
// Additionally, the i-th element is valid because each element is visited at most once
// and it is the first time we access vec[i].
//
// Note: we can't use `vec.get_unchecked_mut(i)` here since the precondition for that
// function is that i < vec.len(), but we've set vec's length to zero.
let cur = unsafe { &mut *self.vec.as_mut_ptr().add(i) };
let drained = (self.pred)(cur);
// 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;
// SAFETY: We never touch this element again after returning it.
return Some(unsafe { ptr::read(cur) });
} else if self.del > 0 {
// SAFETY: `self.del` > 0, so the hole slot must not overlap with current element.
// We use copy for move, and never touch this element again.
unsafe {
let hole_slot = self.vec.as_mut_ptr().add(i - self.del);
ptr::copy_nonoverlapping(cur, hole_slot, 1);
}
}
}
None
}
fn size_hint(&self) -> (usize, Option<usize>) {
(0, Some(self.end - self.idx))
}
}
#[stable(feature = "extract_if", since = "1.87.0")]
impl<T, F, A: Allocator> Drop for ExtractIf<'_, T, F, A> {
fn drop(&mut self) {
if self.del > 0 {
// SAFETY: Trailing unchecked items must be valid since we never touch them.
unsafe {
ptr::copy(
self.vec.as_ptr().add(self.idx),
self.vec.as_mut_ptr().add(self.idx - self.del),
self.old_len - self.idx,
);
}
}
// SAFETY: After filling holes, all items are in contiguous memory.
unsafe {
self.vec.set_len(self.old_len - self.del);
}
}
}
#[stable(feature = "extract_if", since = "1.87.0")]
impl<T, F, A> fmt::Debug for ExtractIf<'_, T, F, A>
where
T: fmt::Debug,
A: Allocator,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let peek = if self.idx < self.end { self.vec.get(self.idx) } else { None };
f.debug_struct("ExtractIf").field("peek", &peek).finish_non_exhaustive()
}
}
|
