1use crate::iter::adapters::SourceIter;
2use crate::iter::{FusedIterator, InPlaceIterable, TrustedFused};
3use crate::mem::{ManuallyDrop, MaybeUninit};
4use crate::num::NonZero;
5use crate::ops::{ControlFlow, Try};
6use crate::{array, fmt};
7
8/// An iterator that uses `f` to both filter and map elements from `iter`.
9///
10/// This `struct` is created by the [`filter_map`] method on [`Iterator`]. See its
11/// documentation for more.
12///
13/// [`filter_map`]: Iterator::filter_map
14/// [`Iterator`]: trait.Iterator.html
15#[must_use = "iterators are lazy and do nothing unless consumed"]
16#[stable(feature = "rust1", since = "1.0.0")]
17#[derive(Clone)]
18pub struct FilterMap<I, F> {
19 iter: I,
20 f: F,
21}
22impl<I, F> FilterMap<I, F> {
23 pub(in crate::iter) fn new(iter: I, f: F) -> FilterMap<I, F> {
24 FilterMap { iter, f }
25 }
26}
27
28#[stable(feature = "core_impl_debug", since = "1.9.0")]
29impl<I: fmt::Debug, F> fmt::Debug for FilterMap<I, F> {
30 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
31 f.debug_struct("FilterMap").field(name:"iter", &self.iter).finish()
32 }
33}
34
35fn filter_map_fold<T, B, Acc>(
36 mut f: impl FnMut(T) -> Option<B>,
37 mut fold: impl FnMut(Acc, B) -> Acc,
38) -> impl FnMut(Acc, T) -> Acc {
39 move |acc: Acc, item: T| match f(item) {
40 Some(x: B) => fold(acc, x),
41 None => acc,
42 }
43}
44
45fn filter_map_try_fold<'a, T, B, Acc, R: Try<Output = Acc>>(
46 f: &'a mut impl FnMut(T) -> Option<B>,
47 mut fold: impl FnMut(Acc, B) -> R + 'a,
48) -> impl FnMut(Acc, T) -> R + 'a {
49 move |acc: Acc, item: T| match f(item) {
50 Some(x: B) => fold(acc, x),
51 None => try { acc },
52 }
53}
54
55#[stable(feature = "rust1", since = "1.0.0")]
56impl<B, I: Iterator, F> Iterator for FilterMap<I, F>
57where
58 F: FnMut(I::Item) -> Option<B>,
59{
60 type Item = B;
61
62 #[inline]
63 fn next(&mut self) -> Option<B> {
64 self.iter.find_map(&mut self.f)
65 }
66
67 #[inline]
68 fn next_chunk<const N: usize>(
69 &mut self,
70 ) -> Result<[Self::Item; N], array::IntoIter<Self::Item, N>> {
71 let mut array: [MaybeUninit<Self::Item>; N] = [const { MaybeUninit::uninit() }; N];
72
73 struct Guard<'a, T> {
74 array: &'a mut [MaybeUninit<T>],
75 initialized: usize,
76 }
77
78 impl<T> Drop for Guard<'_, T> {
79 #[inline]
80 fn drop(&mut self) {
81 if const { crate::mem::needs_drop::<T>() } {
82 // SAFETY: self.initialized is always <= N, which also is the length of the array.
83 unsafe {
84 self.array.get_unchecked_mut(..self.initialized).assume_init_drop();
85 }
86 }
87 }
88 }
89
90 let mut guard = Guard { array: &mut array, initialized: 0 };
91
92 let result = self.iter.try_for_each(|element| {
93 let idx = guard.initialized;
94 let val = (self.f)(element);
95 guard.initialized = idx + val.is_some() as usize;
96
97 // SAFETY: Loop conditions ensure the index is in bounds.
98
99 unsafe {
100 let opt_payload_at: *const MaybeUninit<B> =
101 (&raw const val).byte_add(core::mem::offset_of!(Option<B>, Some.0)).cast();
102 let dst = guard.array.as_mut_ptr().add(idx);
103 crate::ptr::copy_nonoverlapping(opt_payload_at, dst, 1);
104 crate::mem::forget(val);
105 };
106
107 if guard.initialized < N { ControlFlow::Continue(()) } else { ControlFlow::Break(()) }
108 });
109
110 let guard = ManuallyDrop::new(guard);
111
112 match result {
113 ControlFlow::Break(()) => {
114 // SAFETY: The loop above is only explicitly broken when the array has been fully initialized
115 Ok(unsafe { MaybeUninit::array_assume_init(array) })
116 }
117 ControlFlow::Continue(()) => {
118 let initialized = guard.initialized;
119 // SAFETY: The range is in bounds since the loop breaks when reaching N elements.
120 Err(unsafe { array::IntoIter::new_unchecked(array, 0..initialized) })
121 }
122 }
123 }
124
125 #[inline]
126 fn size_hint(&self) -> (usize, Option<usize>) {
127 let (_, upper) = self.iter.size_hint();
128 (0, upper) // can't know a lower bound, due to the predicate
129 }
130
131 #[inline]
132 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
133 where
134 Self: Sized,
135 Fold: FnMut(Acc, Self::Item) -> R,
136 R: Try<Output = Acc>,
137 {
138 self.iter.try_fold(init, filter_map_try_fold(&mut self.f, fold))
139 }
140
141 #[inline]
142 fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
143 where
144 Fold: FnMut(Acc, Self::Item) -> Acc,
145 {
146 self.iter.fold(init, filter_map_fold(self.f, fold))
147 }
148}
149
150#[stable(feature = "rust1", since = "1.0.0")]
151impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for FilterMap<I, F>
152where
153 F: FnMut(I::Item) -> Option<B>,
154{
155 #[inline]
156 fn next_back(&mut self) -> Option<B> {
157 #[inline]
158 fn find<T, B>(
159 f: &mut impl FnMut(T) -> Option<B>,
160 ) -> impl FnMut((), T) -> ControlFlow<B> + '_ {
161 move |(), x| match f(x) {
162 Some(x) => ControlFlow::Break(x),
163 None => ControlFlow::Continue(()),
164 }
165 }
166
167 self.iter.try_rfold((), find(&mut self.f)).break_value()
168 }
169
170 #[inline]
171 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
172 where
173 Self: Sized,
174 Fold: FnMut(Acc, Self::Item) -> R,
175 R: Try<Output = Acc>,
176 {
177 self.iter.try_rfold(init, filter_map_try_fold(&mut self.f, fold))
178 }
179
180 #[inline]
181 fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
182 where
183 Fold: FnMut(Acc, Self::Item) -> Acc,
184 {
185 self.iter.rfold(init, filter_map_fold(self.f, fold))
186 }
187}
188
189#[stable(feature = "fused", since = "1.26.0")]
190impl<B, I: FusedIterator, F> FusedIterator for FilterMap<I, F> where F: FnMut(I::Item) -> Option<B> {}
191
192#[unstable(issue = "none", feature = "trusted_fused")]
193unsafe impl<I: TrustedFused, F> TrustedFused for FilterMap<I, F> {}
194
195#[unstable(issue = "none", feature = "inplace_iteration")]
196unsafe impl<I, F> SourceIter for FilterMap<I, F>
197where
198 I: SourceIter,
199{
200 type Source = I::Source;
201
202 #[inline]
203 unsafe fn as_inner(&mut self) -> &mut I::Source {
204 // SAFETY: unsafe function forwarding to unsafe function with the same requirements
205 unsafe { SourceIter::as_inner(&mut self.iter) }
206 }
207}
208
209#[unstable(issue = "none", feature = "inplace_iteration")]
210unsafe impl<I: InPlaceIterable, F> InPlaceIterable for FilterMap<I, F> {
211 const EXPAND_BY: Option<NonZero<usize>> = I::EXPAND_BY;
212 const MERGE_BY: Option<NonZero<usize>> = I::MERGE_BY;
213}
214