| 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 {} |
| |
| /// Fuse the iterator if the expression is `None`. |
| macro_rules! fuse { |
| ($self:ident . iter . $($call:tt)+) => { |
| match $self.iter { |
| Some(ref mut iter) => match iter.$($call)+ { |
| None => { |
| $self.iter = None; |
| None |
| } |
| item => item, |
| }, |
| None => None, |
| } |
| }; |
| } |
| |
| #[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> { |
| fuse!(self.iter.next()) |
| } |
| |
| #[inline] |
| default fn nth(&mut self, n: usize) -> Option<I::Item> { |
| fuse!(self.iter.nth(n)) |
| } |
| |
| #[inline] |
| default fn last(self) -> Option<I::Item> { |
| match self.iter { |
| Some(iter) => iter.last(), |
| None => None, |
| } |
| } |
| |
| #[inline] |
| default fn count(self) -> usize { |
| match self.iter { |
| Some(iter) => iter.count(), |
| None => 0, |
| } |
| } |
| |
| #[inline] |
| default fn size_hint(&self) -> (usize, Option<usize>) { |
| match self.iter { |
| Some(ref iter) => iter.size_hint(), |
| None => (0, Some(0)), |
| } |
| } |
| |
| #[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, |
| { |
| fuse!(self.iter.find(predicate)) |
| } |
| } |
| |
| #[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> { |
| fuse!(self.iter.next_back()) |
| } |
| |
| #[inline] |
| default fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item> { |
| fuse!(self.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<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, |
| { |
| fuse!(self.iter.rfind(predicate)) |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<I> ExactSizeIterator for Fuse<I> |
| where |
| I: ExactSizeIterator, |
| { |
| default fn len(&self) -> usize { |
| match self.iter { |
| Some(ref iter) => iter.len(), |
| None => 0, |
| } |
| } |
| |
| default fn is_empty(&self) -> bool { |
| match self.iter { |
| Some(ref iter) => iter.is_empty(), |
| None => true, |
| } |
| } |
| } |
| |
| // NOTE: for `I: FusedIterator`, we assume that the iterator is always `Some`. |
| // Implementing this as a directly-expanded macro helps codegen performance. |
| macro_rules! unchecked { |
| ($self:ident) => { |
| match $self { |
| Fuse { iter: Some(iter) } => iter, |
| // SAFETY: the specialized iterator never sets `None` |
| Fuse { iter: 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> { |
| unchecked!(self).next() |
| } |
| |
| #[inline] |
| fn nth(&mut self, n: usize) -> Option<I::Item> { |
| unchecked!(self).nth(n) |
| } |
| |
| #[inline] |
| fn last(self) -> Option<I::Item> { |
| unchecked!(self).last() |
| } |
| |
| #[inline] |
| fn count(self) -> usize { |
| unchecked!(self).count() |
| } |
| |
| #[inline] |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| unchecked!(self).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>, |
| { |
| unchecked!(self).try_fold(init, fold) |
| } |
| |
| #[inline] |
| fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc |
| where |
| Fold: FnMut(Acc, Self::Item) -> Acc, |
| { |
| unchecked!(self).fold(init, fold) |
| } |
| |
| #[inline] |
| fn find<P>(&mut self, predicate: P) -> Option<Self::Item> |
| where |
| P: FnMut(&Self::Item) -> bool, |
| { |
| unchecked!(self).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> { |
| unchecked!(self).next_back() |
| } |
| |
| #[inline] |
| fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item> { |
| unchecked!(self).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>, |
| { |
| unchecked!(self).try_rfold(init, fold) |
| } |
| |
| #[inline] |
| fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc |
| where |
| Fold: FnMut(Acc, Self::Item) -> Acc, |
| { |
| unchecked!(self).rfold(init, fold) |
| } |
| |
| #[inline] |
| fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> |
| where |
| P: FnMut(&Self::Item) -> bool, |
| { |
| unchecked!(self).rfind(predicate) |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<I> ExactSizeIterator for Fuse<I> |
| where |
| I: ExactSizeIterator + FusedIterator, |
| { |
| fn len(&self) -> usize { |
| unchecked!(self).len() |
| } |
| |
| fn is_empty(&self) -> bool { |
| unchecked!(self).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() |
| } |
| } |