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: usize = vec.len();
42 let Range { start: usize, end: usize } = slice::range(range, ..old_len);
43
44 // Guard against the vec getting leaked (leak amplification)
45 unsafe {
46 vec.set_len(new_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: *mut T = self.vec.as_mut_ptr();
101 let src: *mut T = ptr.add(self.idx);
102 let dst: *mut T = src.sub(self.del);
103 let tail_len: usize = self.old_len - self.idx;
104 src.copy_to(dest:dst, count: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: Option<&T> = if self.idx < self.end { self.vec.get(self.idx) } else { None };
119 f.debug_struct("ExtractIf").field(name:"peek", &peek).finish_non_exhaustive()
120 }
121}
122