| use crate::fmt; |
| use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable}; |
| use crate::ops::Try; |
| use core::array; |
| use core::mem::{ManuallyDrop, MaybeUninit}; |
| use core::ops::ControlFlow; |
| |
| /// An iterator that filters the elements of `iter` with `predicate`. |
| /// |
| /// This `struct` is created by the [`filter`] method on [`Iterator`]. See its |
| /// documentation for more. |
| /// |
| /// [`filter`]: Iterator::filter |
| /// [`Iterator`]: trait.Iterator.html |
| #[must_use = "iterators are lazy and do nothing unless consumed"] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[derive(Clone)] |
| pub struct Filter<I, P> { |
| // Used for `SplitWhitespace` and `SplitAsciiWhitespace` `as_str` methods |
| pub(crate) iter: I, |
| predicate: P, |
| } |
| impl<I, P> Filter<I, P> { |
| pub(in crate::iter) fn new(iter: I, predicate: P) -> Filter<I, P> { |
| Filter { iter, predicate } |
| } |
| } |
| |
| #[stable(feature = "core_impl_debug", since = "1.9.0")] |
| impl<I: fmt::Debug, P> fmt::Debug for Filter<I, P> { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| f.debug_struct("Filter").field("iter", &self.iter).finish() |
| } |
| } |
| |
| fn filter_fold<T, Acc>( |
| mut predicate: impl FnMut(&T) -> bool, |
| mut fold: impl FnMut(Acc, T) -> Acc, |
| ) -> impl FnMut(Acc, T) -> Acc { |
| move |acc, item| if predicate(&item) { fold(acc, item) } else { acc } |
| } |
| |
| fn filter_try_fold<'a, T, Acc, R: Try<Output = Acc>>( |
| predicate: &'a mut impl FnMut(&T) -> bool, |
| mut fold: impl FnMut(Acc, T) -> R + 'a, |
| ) -> impl FnMut(Acc, T) -> R + 'a { |
| move |acc, item| if predicate(&item) { fold(acc, item) } else { try { acc } } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<I: Iterator, P> Iterator for Filter<I, P> |
| where |
| P: FnMut(&I::Item) -> bool, |
| { |
| type Item = I::Item; |
| |
| #[inline] |
| fn next(&mut self) -> Option<I::Item> { |
| self.iter.find(&mut self.predicate) |
| } |
| |
| #[inline] |
| fn next_chunk<const N: usize>( |
| &mut self, |
| ) -> Result<[Self::Item; N], array::IntoIter<Self::Item, N>> { |
| let mut array: [MaybeUninit<Self::Item>; N] = MaybeUninit::uninit_array(); |
| |
| struct Guard<'a, T> { |
| array: &'a mut [MaybeUninit<T>], |
| initialized: usize, |
| } |
| |
| impl<T> Drop for Guard<'_, T> { |
| #[inline] |
| fn drop(&mut self) { |
| if const { crate::mem::needs_drop::<T>() } { |
| // SAFETY: self.initialized is always <= N, which also is the length of the array. |
| unsafe { |
| core::ptr::drop_in_place(MaybeUninit::slice_assume_init_mut( |
| self.array.get_unchecked_mut(..self.initialized), |
| )); |
| } |
| } |
| } |
| } |
| |
| let mut guard = Guard { array: &mut array, initialized: 0 }; |
| |
| let result = self.iter.try_for_each(|element| { |
| let idx = guard.initialized; |
| guard.initialized = idx + (self.predicate)(&element) as usize; |
| |
| // SAFETY: Loop conditions ensure the index is in bounds. |
| unsafe { guard.array.get_unchecked_mut(idx) }.write(element); |
| |
| if guard.initialized < N { ControlFlow::Continue(()) } else { ControlFlow::Break(()) } |
| }); |
| |
| let guard = ManuallyDrop::new(guard); |
| |
| match result { |
| ControlFlow::Break(()) => { |
| // SAFETY: The loop above is only explicitly broken when the array has been fully initialized |
| Ok(unsafe { MaybeUninit::array_assume_init(array) }) |
| } |
| ControlFlow::Continue(()) => { |
| let initialized = guard.initialized; |
| // SAFETY: The range is in bounds since the loop breaks when reaching N elements. |
| Err(unsafe { array::IntoIter::new_unchecked(array, 0..initialized) }) |
| } |
| } |
| } |
| |
| #[inline] |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| let (_, upper) = self.iter.size_hint(); |
| (0, upper) // can't know a lower bound, due to the predicate |
| } |
| |
| // this special case allows the compiler to make `.filter(_).count()` |
| // branchless. Barring perfect branch prediction (which is unattainable in |
| // the general case), this will be much faster in >90% of cases (containing |
| // virtually all real workloads) and only a tiny bit slower in the rest. |
| // |
| // Having this specialization thus allows us to write `.filter(p).count()` |
| // where we would otherwise write `.map(|x| p(x) as usize).sum()`, which is |
| // less readable and also less backwards-compatible to Rust before 1.10. |
| // |
| // Using the branchless version will also simplify the LLVM byte code, thus |
| // leaving more budget for LLVM optimizations. |
| #[inline] |
| fn count(self) -> usize { |
| #[inline] |
| fn to_usize<T>(mut predicate: impl FnMut(&T) -> bool) -> impl FnMut(T) -> usize { |
| move |x| predicate(&x) as usize |
| } |
| |
| self.iter.map(to_usize(self.predicate)).sum() |
| } |
| |
| #[inline] |
| fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R |
| where |
| Self: Sized, |
| Fold: FnMut(Acc, Self::Item) -> R, |
| R: Try<Output = Acc>, |
| { |
| self.iter.try_fold(init, filter_try_fold(&mut self.predicate, fold)) |
| } |
| |
| #[inline] |
| fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc |
| where |
| Fold: FnMut(Acc, Self::Item) -> Acc, |
| { |
| self.iter.fold(init, filter_fold(self.predicate, fold)) |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<I: DoubleEndedIterator, P> DoubleEndedIterator for Filter<I, P> |
| where |
| P: FnMut(&I::Item) -> bool, |
| { |
| #[inline] |
| fn next_back(&mut self) -> Option<I::Item> { |
| self.iter.rfind(&mut self.predicate) |
| } |
| |
| #[inline] |
| fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R |
| where |
| Self: Sized, |
| Fold: FnMut(Acc, Self::Item) -> R, |
| R: Try<Output = Acc>, |
| { |
| self.iter.try_rfold(init, filter_try_fold(&mut self.predicate, fold)) |
| } |
| |
| #[inline] |
| fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc |
| where |
| Fold: FnMut(Acc, Self::Item) -> Acc, |
| { |
| self.iter.rfold(init, filter_fold(self.predicate, fold)) |
| } |
| } |
| |
| #[stable(feature = "fused", since = "1.26.0")] |
| impl<I: FusedIterator, P> FusedIterator for Filter<I, P> where P: FnMut(&I::Item) -> bool {} |
| |
| #[unstable(issue = "none", feature = "inplace_iteration")] |
| unsafe impl<P, I> SourceIter for Filter<I, P> |
| where |
| I: SourceIter, |
| { |
| type Source = I::Source; |
| |
| #[inline] |
| unsafe fn as_inner(&mut self) -> &mut I::Source { |
| // SAFETY: unsafe function forwarding to unsafe function with the same requirements |
| unsafe { SourceIter::as_inner(&mut self.iter) } |
| } |
| } |
| |
| #[unstable(issue = "none", feature = "inplace_iteration")] |
| unsafe impl<I: InPlaceIterable, P> InPlaceIterable for Filter<I, P> where P: FnMut(&I::Item) -> bool {} |
