2 use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable};
5 /// An iterator that filters the elements of `iter` with `predicate`.
7 /// This `struct` is created by the [`filter`] method on [`Iterator`]. See its
8 /// documentation for more.
10 /// [`filter`]: Iterator::filter
11 /// [`Iterator`]: trait.Iterator.html
12 #[must_use = "iterators are lazy and do nothing unless consumed"]
13 #[stable(feature = "rust1", since = "1.0.0")]
15 pub struct Filter<I, P> {
16 // Used for `SplitWhitespace` and `SplitAsciiWhitespace` `as_str` methods
20 impl<I, P> Filter<I, P> {
21 pub(in crate::iter) fn new(iter: I, predicate: P) -> Filter<I, P> {
22 Filter { iter, predicate }
26 #[stable(feature = "core_impl_debug", since = "1.9.0")]
27 impl<I: fmt::Debug, P> fmt::Debug for Filter<I, P> {
28 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
29 f.debug_struct("Filter").field("iter", &self.iter).finish()
33 fn filter_fold<T, Acc>(
34 mut predicate: impl FnMut(&T) -> bool,
35 mut fold: impl FnMut(Acc, T) -> Acc,
36 ) -> impl FnMut(Acc, T) -> Acc {
37 move |acc, item| if predicate(&item) { fold(acc, item) } else { acc }
40 fn filter_try_fold<'a, T, Acc, R: Try<Output = Acc>>(
41 predicate: &'a mut impl FnMut(&T) -> bool,
42 mut fold: impl FnMut(Acc, T) -> R + 'a,
43 ) -> impl FnMut(Acc, T) -> R + 'a {
44 move |acc, item| if predicate(&item) { fold(acc, item) } else { try { acc } }
47 #[stable(feature = "rust1", since = "1.0.0")]
48 impl<I: Iterator, P> Iterator for Filter<I, P>
50 P: FnMut(&I::Item) -> bool,
55 fn next(&mut self) -> Option<I::Item> {
56 self.iter.find(&mut self.predicate)
60 fn size_hint(&self) -> (usize, Option<usize>) {
61 let (_, upper) = self.iter.size_hint();
62 (0, upper) // can't know a lower bound, due to the predicate
65 // this special case allows the compiler to make `.filter(_).count()`
66 // branchless. Barring perfect branch prediction (which is unattainable in
67 // the general case), this will be much faster in >90% of cases (containing
68 // virtually all real workloads) and only a tiny bit slower in the rest.
70 // Having this specialization thus allows us to write `.filter(p).count()`
71 // where we would otherwise write `.map(|x| p(x) as usize).sum()`, which is
72 // less readable and also less backwards-compatible to Rust before 1.10.
74 // Using the branchless version will also simplify the LLVM byte code, thus
75 // leaving more budget for LLVM optimizations.
77 fn count(self) -> usize {
79 fn to_usize<T>(mut predicate: impl FnMut(&T) -> bool) -> impl FnMut(T) -> usize {
80 move |x| predicate(&x) as usize
83 self.iter.map(to_usize(self.predicate)).sum()
87 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
90 Fold: FnMut(Acc, Self::Item) -> R,
93 self.iter.try_fold(init, filter_try_fold(&mut self.predicate, fold))
97 fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
99 Fold: FnMut(Acc, Self::Item) -> Acc,
101 self.iter.fold(init, filter_fold(self.predicate, fold))
105 #[stable(feature = "rust1", since = "1.0.0")]
106 impl<I: DoubleEndedIterator, P> DoubleEndedIterator for Filter<I, P>
108 P: FnMut(&I::Item) -> bool,
111 fn next_back(&mut self) -> Option<I::Item> {
112 self.iter.rfind(&mut self.predicate)
116 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
119 Fold: FnMut(Acc, Self::Item) -> R,
120 R: Try<Output = Acc>,
122 self.iter.try_rfold(init, filter_try_fold(&mut self.predicate, fold))
126 fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
128 Fold: FnMut(Acc, Self::Item) -> Acc,
130 self.iter.rfold(init, filter_fold(self.predicate, fold))
134 #[stable(feature = "fused", since = "1.26.0")]
135 impl<I: FusedIterator, P> FusedIterator for Filter<I, P> where P: FnMut(&I::Item) -> bool {}
137 #[unstable(issue = "none", feature = "inplace_iteration")]
138 unsafe impl<P, I> SourceIter for Filter<I, P>
142 type Source = I::Source;
145 unsafe fn as_inner(&mut self) -> &mut I::Source {
146 // SAFETY: unsafe function forwarding to unsafe function with the same requirements
147 unsafe { SourceIter::as_inner(&mut self.iter) }
151 #[unstable(issue = "none", feature = "inplace_iteration")]
152 unsafe impl<I: InPlaceIterable, P> InPlaceIterable for Filter<I, P> where P: FnMut(&I::Item) -> bool {}