| use crate::intrinsics; |
| use crate::iter::{ |
| DoubleEndedIterator, ExactSizeIterator, FusedIterator, Iterator, TrustedRandomAccess, |
| }; |
| use crate::ops::Try; |
| |
| /// An iterator that yields `None` forever after the underlying iterator |
| /// yields `None` once. |
| /// |
| /// This `struct` is created by the [`fuse`] method on [`Iterator`]. See its |
| /// documentation for more. |
| /// |
| /// [`fuse`]: trait.Iterator.html#method.fuse |
| /// [`Iterator`]: trait.Iterator.html |
| #[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`, this is always assumed `Some`! |
| 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 {} |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<I> Iterator for Fuse<I> |
| where |
| I: Iterator, |
| { |
| type Item = <I as Iterator>::Item; |
| |
| #[inline] |
| default fn next(&mut self) -> Option<<I as Iterator>::Item> { |
| let next = self.iter.as_mut()?.next(); |
| if next.is_none() { |
| self.iter = None; |
| } |
| next |
| } |
| |
| #[inline] |
| default fn nth(&mut self, n: usize) -> Option<I::Item> { |
| let nth = self.iter.as_mut()?.nth(n); |
| if nth.is_none() { |
| self.iter = None; |
| } |
| nth |
| } |
| |
| #[inline] |
| default fn last(self) -> Option<I::Item> { |
| self.iter?.last() |
| } |
| |
| #[inline] |
| default fn count(self) -> usize { |
| self.iter.map_or(0, I::count) |
| } |
| |
| #[inline] |
| default fn size_hint(&self) -> (usize, Option<usize>) { |
| self.iter.as_ref().map_or((0, Some(0)), I::size_hint) |
| } |
| |
| #[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<Ok = Acc>, |
| { |
| if let Some(ref mut iter) = self.iter { |
| acc = iter.try_fold(acc, fold)?; |
| self.iter = None; |
| } |
| Try::from_ok(acc) |
| } |
| |
| #[inline] |
| default 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] |
| default fn find<P>(&mut self, predicate: P) -> Option<Self::Item> |
| where |
| P: FnMut(&Self::Item) -> bool, |
| { |
| let found = self.iter.as_mut()?.find(predicate); |
| if found.is_none() { |
| self.iter = None; |
| } |
| found |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<I> DoubleEndedIterator for Fuse<I> |
| where |
| I: DoubleEndedIterator, |
| { |
| #[inline] |
| default fn next_back(&mut self) -> Option<<I as Iterator>::Item> { |
| let next = self.iter.as_mut()?.next_back(); |
| if next.is_none() { |
| self.iter = None; |
| } |
| next |
| } |
| |
| #[inline] |
| default fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item> { |
| let nth = self.iter.as_mut()?.nth_back(n); |
| if nth.is_none() { |
| self.iter = None; |
| } |
| nth |
| } |
| |
| #[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<Ok = Acc>, |
| { |
| if let Some(ref mut iter) = self.iter { |
| acc = iter.try_rfold(acc, fold)?; |
| self.iter = None; |
| } |
| Try::from_ok(acc) |
| } |
| |
| #[inline] |
| default 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] |
| default fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> |
| where |
| P: FnMut(&Self::Item) -> bool, |
| { |
| let found = self.iter.as_mut()?.rfind(predicate); |
| if found.is_none() { |
| self.iter = None; |
| } |
| found |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<I> ExactSizeIterator for Fuse<I> |
| where |
| I: ExactSizeIterator, |
| { |
| default fn len(&self) -> usize { |
| self.iter.as_ref().map_or(0, I::len) |
| } |
| |
| default fn is_empty(&self) -> bool { |
| self.iter.as_ref().map_or(true, I::is_empty) |
| } |
| } |
| |
| // NOTE: for `I: FusedIterator`, we assume that the iterator is always `Some` |
| impl<I: FusedIterator> Fuse<I> { |
| #[inline(always)] |
| fn as_inner(&self) -> &I { |
| match self.iter { |
| Some(ref iter) => iter, |
| // SAFETY: the specialized iterator never sets `None` |
| None => unsafe { intrinsics::unreachable() }, |
| } |
| } |
| |
| #[inline(always)] |
| fn as_inner_mut(&mut self) -> &mut I { |
| match self.iter { |
| Some(ref mut iter) => iter, |
| // SAFETY: the specialized iterator never sets `None` |
| None => unsafe { intrinsics::unreachable() }, |
| } |
| } |
| |
| #[inline(always)] |
| fn into_inner(self) -> I { |
| match self.iter { |
| Some(iter) => iter, |
| // SAFETY: the specialized iterator never sets `None` |
| None => unsafe { intrinsics::unreachable() }, |
| } |
| } |
| } |
| |
| #[stable(feature = "fused", since = "1.26.0")] |
| impl<I> Iterator for Fuse<I> |
| where |
| I: FusedIterator, |
| { |
| #[inline] |
| fn next(&mut self) -> Option<<I as Iterator>::Item> { |
| self.as_inner_mut().next() |
| } |
| |
| #[inline] |
| fn nth(&mut self, n: usize) -> Option<I::Item> { |
| self.as_inner_mut().nth(n) |
| } |
| |
| #[inline] |
| fn last(self) -> Option<I::Item> { |
| self.into_inner().last() |
| } |
| |
| #[inline] |
| fn count(self) -> usize { |
| self.into_inner().count() |
| } |
| |
| #[inline] |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| self.as_inner().size_hint() |
| } |
| |
| #[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<Ok = Acc>, |
| { |
| self.as_inner_mut().try_fold(init, fold) |
| } |
| |
| #[inline] |
| fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc |
| where |
| Fold: FnMut(Acc, Self::Item) -> Acc, |
| { |
| self.into_inner().fold(init, fold) |
| } |
| |
| #[inline] |
| fn find<P>(&mut self, predicate: P) -> Option<Self::Item> |
| where |
| P: FnMut(&Self::Item) -> bool, |
| { |
| self.as_inner_mut().find(predicate) |
| } |
| } |
| |
| #[stable(feature = "fused", since = "1.26.0")] |
| impl<I> DoubleEndedIterator for Fuse<I> |
| where |
| I: DoubleEndedIterator + FusedIterator, |
| { |
| #[inline] |
| fn next_back(&mut self) -> Option<<I as Iterator>::Item> { |
| self.as_inner_mut().next_back() |
| } |
| |
| #[inline] |
| fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item> { |
| self.as_inner_mut().nth_back(n) |
| } |
| |
| #[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<Ok = Acc>, |
| { |
| self.as_inner_mut().try_rfold(init, fold) |
| } |
| |
| #[inline] |
| fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc |
| where |
| Fold: FnMut(Acc, Self::Item) -> Acc, |
| { |
| self.into_inner().rfold(init, fold) |
| } |
| |
| #[inline] |
| fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> |
| where |
| P: FnMut(&Self::Item) -> bool, |
| { |
| self.as_inner_mut().rfind(predicate) |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<I> ExactSizeIterator for Fuse<I> |
| where |
| I: ExactSizeIterator + FusedIterator, |
| { |
| fn len(&self) -> usize { |
| self.as_inner().len() |
| } |
| |
| fn is_empty(&self) -> bool { |
| self.as_inner().is_empty() |
| } |
| } |
| |
| unsafe impl<I> TrustedRandomAccess for Fuse<I> |
| where |
| I: TrustedRandomAccess, |
| { |
| unsafe fn get_unchecked(&mut self, i: usize) -> I::Item { |
| match self.iter { |
| Some(ref mut iter) => iter.get_unchecked(i), |
| // SAFETY: the caller asserts there is an item at `i`, so we're not exhausted. |
| None => intrinsics::unreachable(), |
| } |
| } |
| |
| fn may_have_side_effect() -> bool { |
| I::may_have_side_effect() |
| } |
| } |