1use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable, TrustedFused};
2use crate::mem::{ManuallyDrop, MaybeUninit};
3use crate::num::NonZero;
4use crate::ops::{ControlFlow, Try};
5use crate::ptr::addr_of;
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] = MaybeUninit::uninit_array();
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 core::ptr::drop_in_place(MaybeUninit::slice_assume_init_mut(
85 self.array.get_unchecked_mut(..self.initialized),
86 ));
87 }
88 }
89 }
90 }
91
92 let mut guard = Guard { array: &mut array, initialized: 0 };
93
94 let result = self.iter.try_for_each(|element| {
95 let idx = guard.initialized;
96 let val = (self.f)(element);
97 guard.initialized = idx + val.is_some() as usize;
98
99 // SAFETY: Loop conditions ensure the index is in bounds.
100
101 unsafe {
102 let opt_payload_at: *const MaybeUninit<B> =
103 addr_of!(val).byte_add(core::mem::offset_of!(Option<B>, Some.0)).cast();
104 let dst = guard.array.as_mut_ptr().add(idx);
105 crate::ptr::copy_nonoverlapping(opt_payload_at, dst, 1);
106 crate::mem::forget(val);
107 };
108
109 if guard.initialized < N { ControlFlow::Continue(()) } else { ControlFlow::Break(()) }
110 });
111
112 let guard = ManuallyDrop::new(guard);
113
114 match result {
115 ControlFlow::Break(()) => {
116 // SAFETY: The loop above is only explicitly broken when the array has been fully initialized
117 Ok(unsafe { MaybeUninit::array_assume_init(array) })
118 }
119 ControlFlow::Continue(()) => {
120 let initialized = guard.initialized;
121 // SAFETY: The range is in bounds since the loop breaks when reaching N elements.
122 Err(unsafe { array::IntoIter::new_unchecked(array, 0..initialized) })
123 }
124 }
125 }
126
127 #[inline]
128 fn size_hint(&self) -> (usize, Option<usize>) {
129 let (_, upper) = self.iter.size_hint();
130 (0, upper) // can't know a lower bound, due to the predicate
131 }
132
133 #[inline]
134 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
135 where
136 Self: Sized,
137 Fold: FnMut(Acc, Self::Item) -> R,
138 R: Try<Output = Acc>,
139 {
140 self.iter.try_fold(init, filter_map_try_fold(&mut self.f, fold))
141 }
142
143 #[inline]
144 fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
145 where
146 Fold: FnMut(Acc, Self::Item) -> Acc,
147 {
148 self.iter.fold(init, filter_map_fold(self.f, fold))
149 }
150}
151
152#[stable(feature = "rust1", since = "1.0.0")]
153impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for FilterMap<I, F>
154where
155 F: FnMut(I::Item) -> Option<B>,
156{
157 #[inline]
158 fn next_back(&mut self) -> Option<B> {
159 #[inline]
160 fn find<T, B>(
161 f: &mut impl FnMut(T) -> Option<B>,
162 ) -> impl FnMut((), T) -> ControlFlow<B> + '_ {
163 move |(), x| match f(x) {
164 Some(x) => ControlFlow::Break(x),
165 None => ControlFlow::Continue(()),
166 }
167 }
168
169 self.iter.try_rfold((), find(&mut self.f)).break_value()
170 }
171
172 #[inline]
173 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
174 where
175 Self: Sized,
176 Fold: FnMut(Acc, Self::Item) -> R,
177 R: Try<Output = Acc>,
178 {
179 self.iter.try_rfold(init, filter_map_try_fold(&mut self.f, fold))
180 }
181
182 #[inline]
183 fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
184 where
185 Fold: FnMut(Acc, Self::Item) -> Acc,
186 {
187 self.iter.rfold(init, filter_map_fold(self.f, fold))
188 }
189}
190
191#[stable(feature = "fused", since = "1.26.0")]
192impl<B, I: FusedIterator, F> FusedIterator for FilterMap<I, F> where F: FnMut(I::Item) -> Option<B> {}
193
194#[unstable(issue = "none", feature = "trusted_fused")]
195unsafe impl<I: TrustedFused, F> TrustedFused for FilterMap<I, F> {}
196
197#[unstable(issue = "none", feature = "inplace_iteration")]
198unsafe impl<I, F> SourceIter for FilterMap<I, F>
199where
200 I: SourceIter,
201{
202 type Source = I::Source;
203
204 #[inline]
205 unsafe fn as_inner(&mut self) -> &mut I::Source {
206 // SAFETY: unsafe function forwarding to unsafe function with the same requirements
207 unsafe { SourceIter::as_inner(&mut self.iter) }
208 }
209}
210
211#[unstable(issue = "none", feature = "inplace_iteration")]
212unsafe impl<I: InPlaceIterable, F> InPlaceIterable for FilterMap<I, F> {
213 const EXPAND_BY: Option<NonZero<usize>> = I::EXPAND_BY;
214 const MERGE_BY: Option<NonZero<usize>> = I::MERGE_BY;
215}
216