154 lines
4.8 KiB
Rust
154 lines
4.8 KiB
Rust
use crate::fmt;
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use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable};
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use crate::ops::Try;
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/// An iterator that filters the elements of `iter` with `predicate`.
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///
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/// This `struct` is created by the [`filter`] method on [`Iterator`]. See its
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/// documentation for more.
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///
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/// [`filter`]: Iterator::filter
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/// [`Iterator`]: trait.Iterator.html
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#[must_use = "iterators are lazy and do nothing unless consumed"]
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#[stable(feature = "rust1", since = "1.0.0")]
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#[derive(Clone)]
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pub struct Filter<I, P> {
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// Used for `SplitWhitespace` and `SplitAsciiWhitespace` `as_str` methods
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pub(crate) iter: I,
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predicate: P,
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}
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impl<I, P> Filter<I, P> {
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pub(in crate::iter) fn new(iter: I, predicate: P) -> Filter<I, P> {
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Filter { iter, predicate }
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}
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}
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#[stable(feature = "core_impl_debug", since = "1.9.0")]
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impl<I: fmt::Debug, P> fmt::Debug for Filter<I, P> {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.debug_struct("Filter").field("iter", &self.iter).finish()
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}
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}
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fn filter_fold<T, Acc>(
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mut predicate: impl FnMut(&T) -> bool,
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mut fold: impl FnMut(Acc, T) -> Acc,
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) -> impl FnMut(Acc, T) -> Acc {
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move |acc, item| if predicate(&item) { fold(acc, item) } else { acc }
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}
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fn filter_try_fold<'a, T, Acc, R: Try<Ok = Acc>>(
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predicate: &'a mut impl FnMut(&T) -> bool,
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mut fold: impl FnMut(Acc, T) -> R + 'a,
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) -> impl FnMut(Acc, T) -> R + 'a {
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move |acc, item| if predicate(&item) { fold(acc, item) } else { try { acc } }
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<I: Iterator, P> Iterator for Filter<I, P>
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where
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P: FnMut(&I::Item) -> bool,
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{
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type Item = I::Item;
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#[inline]
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fn next(&mut self) -> Option<I::Item> {
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self.iter.find(&mut self.predicate)
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}
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#[inline]
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fn size_hint(&self) -> (usize, Option<usize>) {
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let (_, upper) = self.iter.size_hint();
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(0, upper) // can't know a lower bound, due to the predicate
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}
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// this special case allows the compiler to make `.filter(_).count()`
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// branchless. Barring perfect branch prediction (which is unattainable in
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// the general case), this will be much faster in >90% of cases (containing
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// virtually all real workloads) and only a tiny bit slower in the rest.
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//
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// Having this specialization thus allows us to write `.filter(p).count()`
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// where we would otherwise write `.map(|x| p(x) as usize).sum()`, which is
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// less readable and also less backwards-compatible to Rust before 1.10.
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//
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// Using the branchless version will also simplify the LLVM byte code, thus
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// leaving more budget for LLVM optimizations.
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#[inline]
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fn count(self) -> usize {
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#[inline]
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fn to_usize<T>(mut predicate: impl FnMut(&T) -> bool) -> impl FnMut(T) -> usize {
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move |x| predicate(&x) as usize
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}
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self.iter.map(to_usize(self.predicate)).sum()
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}
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#[inline]
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fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
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where
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Self: Sized,
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Fold: FnMut(Acc, Self::Item) -> R,
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R: Try<Ok = Acc>,
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{
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self.iter.try_fold(init, filter_try_fold(&mut self.predicate, fold))
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}
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#[inline]
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fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
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where
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Fold: FnMut(Acc, Self::Item) -> Acc,
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{
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self.iter.fold(init, filter_fold(self.predicate, fold))
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<I: DoubleEndedIterator, P> DoubleEndedIterator for Filter<I, P>
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where
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P: FnMut(&I::Item) -> bool,
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{
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#[inline]
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fn next_back(&mut self) -> Option<I::Item> {
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self.iter.rfind(&mut self.predicate)
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}
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#[inline]
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fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
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where
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Self: Sized,
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Fold: FnMut(Acc, Self::Item) -> R,
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R: Try<Ok = Acc>,
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{
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self.iter.try_rfold(init, filter_try_fold(&mut self.predicate, fold))
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}
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#[inline]
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fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
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where
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Fold: FnMut(Acc, Self::Item) -> Acc,
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{
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self.iter.rfold(init, filter_fold(self.predicate, fold))
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}
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}
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#[stable(feature = "fused", since = "1.26.0")]
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impl<I: FusedIterator, P> FusedIterator for Filter<I, P> where P: FnMut(&I::Item) -> bool {}
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#[unstable(issue = "none", feature = "inplace_iteration")]
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unsafe impl<S: Iterator, P, I: Iterator> SourceIter for Filter<I, P>
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where
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P: FnMut(&I::Item) -> bool,
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I: SourceIter<Source = S>,
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{
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type Source = S;
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#[inline]
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unsafe fn as_inner(&mut self) -> &mut S {
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// SAFETY: unsafe function forwarding to unsafe function with the same requirements
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unsafe { SourceIter::as_inner(&mut self.iter) }
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}
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}
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#[unstable(issue = "none", feature = "inplace_iteration")]
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unsafe impl<I: InPlaceIterable, P> InPlaceIterable for Filter<I, P> where P: FnMut(&I::Item) -> bool {}
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