| use crate::intrinsics; |
| use crate::iter::adapters::zip::try_get_unchecked; |
| use crate::iter::{ |
| DoubleEndedIterator, ExactSizeIterator, FusedIterator, TrustedLen, TrustedRandomAccess, |
| TrustedRandomAccessNoCoerce, |
| }; |
| use crate::ops::Try; |
| |
| /// An iterator that yields `None` forever after the underlying iterator |
| /// yields `None` once. |
| /// |
| /// This `struct` is created by [`Iterator::fuse`]. See its documentation |
| /// for more. |
| #[derive(Clone, Debug)] |
| #[must_use = "iterators are lazy and do nothing unless consumed"] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub struct Fuse<I> { |
| // NOTE: for `I: FusedIterator`, we never bother setting `None`, but |
| // we still have to be prepared for that state due to variance. |
| // See rust-lang/rust#85863 |
| iter: Option<I>, |
| } |
| impl<I> Fuse<I> { |
| pub(in crate::iter) fn new(iter: I) -> Fuse<I> { |
| Fuse { iter: Some(iter) } |
| } |
| } |
| |
| #[stable(feature = "fused", since = "1.26.0")] |
| impl<I> FusedIterator for Fuse<I> where I: Iterator {} |
| |
| // Any specialized implementation here is made internal |
| // to avoid exposing default fns outside this trait. |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<I> Iterator for Fuse<I> |
| where |
| I: Iterator, |
| { |
| type Item = <I as Iterator>::Item; |
| |
| #[inline] |
| fn next(&mut self) -> Option<Self::Item> { |
| FuseImpl::next(self) |
| } |
| |
| #[inline] |
| fn nth(&mut self, n: usize) -> Option<I::Item> { |
| FuseImpl::nth(self, n) |
| } |
| |
| #[inline] |
| fn last(self) -> Option<Self::Item> { |
| match self.iter { |
| Some(iter) => iter.last(), |
| None => None, |
| } |
| } |
| |
| #[inline] |
| fn count(self) -> usize { |
| match self.iter { |
| Some(iter) => iter.count(), |
| None => 0, |
| } |
| } |
| |
| #[inline] |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| match self.iter { |
| Some(ref iter) => iter.size_hint(), |
| None => (0, Some(0)), |
| } |
| } |
| |
| #[inline] |
| fn try_fold<Acc, Fold, R>(&mut self, acc: Acc, fold: Fold) -> R |
| where |
| Self: Sized, |
| Fold: FnMut(Acc, Self::Item) -> R, |
| R: Try<Output = Acc>, |
| { |
| FuseImpl::try_fold(self, acc, fold) |
| } |
| |
| #[inline] |
| fn fold<Acc, Fold>(self, mut acc: Acc, fold: Fold) -> Acc |
| where |
| Fold: FnMut(Acc, Self::Item) -> Acc, |
| { |
| if let Some(iter) = self.iter { |
| acc = iter.fold(acc, fold); |
| } |
| acc |
| } |
| |
| #[inline] |
| fn find<P>(&mut self, predicate: P) -> Option<Self::Item> |
| where |
| P: FnMut(&Self::Item) -> bool, |
| { |
| FuseImpl::find(self, predicate) |
| } |
| |
| #[inline] |
| unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item |
| where |
| Self: TrustedRandomAccessNoCoerce, |
| { |
| match self.iter { |
| // SAFETY: the caller must uphold the contract for |
| // `Iterator::__iterator_get_unchecked`. |
| Some(ref mut iter) => unsafe { try_get_unchecked(iter, idx) }, |
| // SAFETY: the caller asserts there is an item at `i`, so we're not exhausted. |
| None => unsafe { intrinsics::unreachable() }, |
| } |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<I> DoubleEndedIterator for Fuse<I> |
| where |
| I: DoubleEndedIterator, |
| { |
| #[inline] |
| fn next_back(&mut self) -> Option<<I as Iterator>::Item> { |
| FuseImpl::next_back(self) |
| } |
| |
| #[inline] |
| fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item> { |
| FuseImpl::nth_back(self, n) |
| } |
| |
| #[inline] |
| fn try_rfold<Acc, Fold, R>(&mut self, acc: Acc, fold: Fold) -> R |
| where |
| Self: Sized, |
| Fold: FnMut(Acc, Self::Item) -> R, |
| R: Try<Output = Acc>, |
| { |
| FuseImpl::try_rfold(self, acc, fold) |
| } |
| |
| #[inline] |
| fn rfold<Acc, Fold>(self, mut acc: Acc, fold: Fold) -> Acc |
| where |
| Fold: FnMut(Acc, Self::Item) -> Acc, |
| { |
| if let Some(iter) = self.iter { |
| acc = iter.rfold(acc, fold); |
| } |
| acc |
| } |
| |
| #[inline] |
| fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> |
| where |
| P: FnMut(&Self::Item) -> bool, |
| { |
| FuseImpl::rfind(self, predicate) |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<I> ExactSizeIterator for Fuse<I> |
| where |
| I: ExactSizeIterator, |
| { |
| fn len(&self) -> usize { |
| match self.iter { |
| Some(ref iter) => iter.len(), |
| None => 0, |
| } |
| } |
| |
| fn is_empty(&self) -> bool { |
| match self.iter { |
| Some(ref iter) => iter.is_empty(), |
| None => true, |
| } |
| } |
| } |
| |
| #[unstable(feature = "trusted_len", issue = "37572")] |
| // SAFETY: `TrustedLen` requires that an accurate length is reported via `size_hint()`. As `Fuse` |
| // is just forwarding this to the wrapped iterator `I` this property is preserved and it is safe to |
| // implement `TrustedLen` here. |
| unsafe impl<I> TrustedLen for Fuse<I> where I: TrustedLen {} |
| |
| #[doc(hidden)] |
| #[unstable(feature = "trusted_random_access", issue = "none")] |
| // SAFETY: `TrustedRandomAccess` requires that `size_hint()` must be exact and cheap to call, and |
| // `Iterator::__iterator_get_unchecked()` must be implemented accordingly. |
| // |
| // This is safe to implement as `Fuse` is just forwarding these to the wrapped iterator `I`, which |
| // preserves these properties. |
| unsafe impl<I> TrustedRandomAccess for Fuse<I> where I: TrustedRandomAccess {} |
| |
| #[doc(hidden)] |
| #[unstable(feature = "trusted_random_access", issue = "none")] |
| unsafe impl<I> TrustedRandomAccessNoCoerce for Fuse<I> |
| where |
| I: TrustedRandomAccessNoCoerce, |
| { |
| const MAY_HAVE_SIDE_EFFECT: bool = I::MAY_HAVE_SIDE_EFFECT; |
| } |
| |
| /// Fuse specialization trait |
| /// |
| /// We only need to worry about `&mut self` methods, which |
| /// may exhaust the iterator without consuming it. |
| #[doc(hidden)] |
| trait FuseImpl<I> { |
| type Item; |
| |
| // Functions specific to any normal Iterators |
| fn next(&mut self) -> Option<Self::Item>; |
| fn nth(&mut self, n: usize) -> Option<Self::Item>; |
| fn try_fold<Acc, Fold, R>(&mut self, acc: Acc, fold: Fold) -> R |
| where |
| Self: Sized, |
| Fold: FnMut(Acc, Self::Item) -> R, |
| R: Try<Output = Acc>; |
| fn find<P>(&mut self, predicate: P) -> Option<Self::Item> |
| where |
| P: FnMut(&Self::Item) -> bool; |
| |
| // Functions specific to DoubleEndedIterators |
| fn next_back(&mut self) -> Option<Self::Item> |
| where |
| I: DoubleEndedIterator; |
| fn nth_back(&mut self, n: usize) -> Option<Self::Item> |
| where |
| I: DoubleEndedIterator; |
| fn try_rfold<Acc, Fold, R>(&mut self, acc: Acc, fold: Fold) -> R |
| where |
| Self: Sized, |
| Fold: FnMut(Acc, Self::Item) -> R, |
| R: Try<Output = Acc>, |
| I: DoubleEndedIterator; |
| fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> |
| where |
| P: FnMut(&Self::Item) -> bool, |
| I: DoubleEndedIterator; |
| } |
| |
| /// General `Fuse` impl which sets `iter = None` when exhausted. |
| #[doc(hidden)] |
| impl<I> FuseImpl<I> for Fuse<I> |
| where |
| I: Iterator, |
| { |
| type Item = <I as Iterator>::Item; |
| |
| #[inline] |
| default fn next(&mut self) -> Option<<I as Iterator>::Item> { |
| and_then_or_clear(&mut self.iter, Iterator::next) |
| } |
| |
| #[inline] |
| default fn nth(&mut self, n: usize) -> Option<I::Item> { |
| and_then_or_clear(&mut self.iter, |iter| iter.nth(n)) |
| } |
| |
| #[inline] |
| default fn try_fold<Acc, Fold, R>(&mut self, mut acc: Acc, fold: Fold) -> R |
| where |
| Self: Sized, |
| Fold: FnMut(Acc, Self::Item) -> R, |
| R: Try<Output = Acc>, |
| { |
| if let Some(ref mut iter) = self.iter { |
| acc = iter.try_fold(acc, fold)?; |
| self.iter = None; |
| } |
| try { acc } |
| } |
| |
| #[inline] |
| default fn find<P>(&mut self, predicate: P) -> Option<Self::Item> |
| where |
| P: FnMut(&Self::Item) -> bool, |
| { |
| and_then_or_clear(&mut self.iter, |iter| iter.find(predicate)) |
| } |
| |
| #[inline] |
| default fn next_back(&mut self) -> Option<<I as Iterator>::Item> |
| where |
| I: DoubleEndedIterator, |
| { |
| and_then_or_clear(&mut self.iter, |iter| iter.next_back()) |
| } |
| |
| #[inline] |
| default fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item> |
| where |
| I: DoubleEndedIterator, |
| { |
| and_then_or_clear(&mut self.iter, |iter| iter.nth_back(n)) |
| } |
| |
| #[inline] |
| default fn try_rfold<Acc, Fold, R>(&mut self, mut acc: Acc, fold: Fold) -> R |
| where |
| Self: Sized, |
| Fold: FnMut(Acc, Self::Item) -> R, |
| R: Try<Output = Acc>, |
| I: DoubleEndedIterator, |
| { |
| if let Some(ref mut iter) = self.iter { |
| acc = iter.try_rfold(acc, fold)?; |
| self.iter = None; |
| } |
| try { acc } |
| } |
| |
| #[inline] |
| default fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> |
| where |
| P: FnMut(&Self::Item) -> bool, |
| I: DoubleEndedIterator, |
| { |
| and_then_or_clear(&mut self.iter, |iter| iter.rfind(predicate)) |
| } |
| } |
| |
| /// Specialized `Fuse` impl which doesn't bother clearing `iter` when exhausted. |
| /// However, we must still be prepared for the possibility that it was already cleared! |
| #[doc(hidden)] |
| impl<I> FuseImpl<I> for Fuse<I> |
| where |
| I: FusedIterator, |
| { |
| #[inline] |
| fn next(&mut self) -> Option<<I as Iterator>::Item> { |
| self.iter.as_mut()?.next() |
| } |
| |
| #[inline] |
| fn nth(&mut self, n: usize) -> Option<I::Item> { |
| self.iter.as_mut()?.nth(n) |
| } |
| |
| #[inline] |
| fn try_fold<Acc, Fold, R>(&mut self, mut acc: Acc, fold: Fold) -> R |
| where |
| Self: Sized, |
| Fold: FnMut(Acc, Self::Item) -> R, |
| R: Try<Output = Acc>, |
| { |
| if let Some(ref mut iter) = self.iter { |
| acc = iter.try_fold(acc, fold)?; |
| } |
| try { acc } |
| } |
| |
| #[inline] |
| fn find<P>(&mut self, predicate: P) -> Option<Self::Item> |
| where |
| P: FnMut(&Self::Item) -> bool, |
| { |
| self.iter.as_mut()?.find(predicate) |
| } |
| |
| #[inline] |
| fn next_back(&mut self) -> Option<<I as Iterator>::Item> |
| where |
| I: DoubleEndedIterator, |
| { |
| self.iter.as_mut()?.next_back() |
| } |
| |
| #[inline] |
| fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item> |
| where |
| I: DoubleEndedIterator, |
| { |
| self.iter.as_mut()?.nth_back(n) |
| } |
| |
| #[inline] |
| fn try_rfold<Acc, Fold, R>(&mut self, mut acc: Acc, fold: Fold) -> R |
| where |
| Self: Sized, |
| Fold: FnMut(Acc, Self::Item) -> R, |
| R: Try<Output = Acc>, |
| I: DoubleEndedIterator, |
| { |
| if let Some(ref mut iter) = self.iter { |
| acc = iter.try_rfold(acc, fold)?; |
| } |
| try { acc } |
| } |
| |
| #[inline] |
| fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> |
| where |
| P: FnMut(&Self::Item) -> bool, |
| I: DoubleEndedIterator, |
| { |
| self.iter.as_mut()?.rfind(predicate) |
| } |
| } |
| |
| #[inline] |
| fn and_then_or_clear<T, U>(opt: &mut Option<T>, f: impl FnOnce(&mut T) -> Option<U>) -> Option<U> { |
| let x = f(opt.as_mut()?); |
| if x.is_none() { |
| *opt = None; |
| } |
| x |
| } |