| use crate::iter::adapters::{ |
| zip::try_get_unchecked, SourceIter, TrustedRandomAccess, TrustedRandomAccessNoCoerce, |
| }; |
| use crate::iter::{FusedIterator, InPlaceIterable, TrustedLen}; |
| use crate::ops::Try; |
| |
| /// An iterator that yields the current count and the element during iteration. |
| /// |
| /// This `struct` is created by the [`enumerate`] method on [`Iterator`]. See its |
| /// documentation for more. |
| /// |
| /// [`enumerate`]: Iterator::enumerate |
| /// [`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 Enumerate<I> { |
| iter: I, |
| count: usize, |
| } |
| impl<I> Enumerate<I> { |
| pub(in crate::iter) fn new(iter: I) -> Enumerate<I> { |
| Enumerate { iter, count: 0 } |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<I> Iterator for Enumerate<I> |
| where |
| I: Iterator, |
| { |
| type Item = (usize, <I as Iterator>::Item); |
| |
| /// # Overflow Behavior |
| /// |
| /// The method does no guarding against overflows, so enumerating more than |
| /// `usize::MAX` elements either produces the wrong result or panics. If |
| /// debug assertions are enabled, a panic is guaranteed. |
| /// |
| /// # Panics |
| /// |
| /// Might panic if the index of the element overflows a `usize`. |
| #[inline] |
| #[rustc_inherit_overflow_checks] |
| fn next(&mut self) -> Option<(usize, <I as Iterator>::Item)> { |
| let a = self.iter.next()?; |
| let i = self.count; |
| self.count += 1; |
| Some((i, a)) |
| } |
| |
| #[inline] |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| self.iter.size_hint() |
| } |
| |
| #[inline] |
| #[rustc_inherit_overflow_checks] |
| fn nth(&mut self, n: usize) -> Option<(usize, I::Item)> { |
| let a = self.iter.nth(n)?; |
| let i = self.count + n; |
| self.count = i + 1; |
| Some((i, a)) |
| } |
| |
| #[inline] |
| fn count(self) -> usize { |
| self.iter.count() |
| } |
| |
| #[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>, |
| { |
| #[inline] |
| fn enumerate<'a, T, Acc, R>( |
| count: &'a mut usize, |
| mut fold: impl FnMut(Acc, (usize, T)) -> R + 'a, |
| ) -> impl FnMut(Acc, T) -> R + 'a { |
| #[rustc_inherit_overflow_checks] |
| move |acc, item| { |
| let acc = fold(acc, (*count, item)); |
| *count += 1; |
| acc |
| } |
| } |
| |
| self.iter.try_fold(init, enumerate(&mut self.count, fold)) |
| } |
| |
| #[inline] |
| fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc |
| where |
| Fold: FnMut(Acc, Self::Item) -> Acc, |
| { |
| #[inline] |
| fn enumerate<T, Acc>( |
| mut count: usize, |
| mut fold: impl FnMut(Acc, (usize, T)) -> Acc, |
| ) -> impl FnMut(Acc, T) -> Acc { |
| #[rustc_inherit_overflow_checks] |
| move |acc, item| { |
| let acc = fold(acc, (count, item)); |
| count += 1; |
| acc |
| } |
| } |
| |
| self.iter.fold(init, enumerate(self.count, fold)) |
| } |
| |
| #[inline] |
| #[rustc_inherit_overflow_checks] |
| fn advance_by(&mut self, n: usize) -> Result<(), usize> { |
| match self.iter.advance_by(n) { |
| ret @ Ok(_) => { |
| self.count += n; |
| ret |
| } |
| ret @ Err(advanced) => { |
| self.count += advanced; |
| ret |
| } |
| } |
| } |
| |
| #[rustc_inherit_overflow_checks] |
| #[inline] |
| unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> <Self as Iterator>::Item |
| where |
| Self: TrustedRandomAccessNoCoerce, |
| { |
| // SAFETY: the caller must uphold the contract for |
| // `Iterator::__iterator_get_unchecked`. |
| let value = unsafe { try_get_unchecked(&mut self.iter, idx) }; |
| (self.count + idx, value) |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<I> DoubleEndedIterator for Enumerate<I> |
| where |
| I: ExactSizeIterator + DoubleEndedIterator, |
| { |
| #[inline] |
| fn next_back(&mut self) -> Option<(usize, <I as Iterator>::Item)> { |
| let a = self.iter.next_back()?; |
| let len = self.iter.len(); |
| // Can safely add, `ExactSizeIterator` promises that the number of |
| // elements fits into a `usize`. |
| Some((self.count + len, a)) |
| } |
| |
| #[inline] |
| fn nth_back(&mut self, n: usize) -> Option<(usize, <I as Iterator>::Item)> { |
| let a = self.iter.nth_back(n)?; |
| let len = self.iter.len(); |
| // Can safely add, `ExactSizeIterator` promises that the number of |
| // elements fits into a `usize`. |
| Some((self.count + len, a)) |
| } |
| |
| #[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>, |
| { |
| // Can safely add and subtract the count, as `ExactSizeIterator` promises |
| // that the number of elements fits into a `usize`. |
| fn enumerate<T, Acc, R>( |
| mut count: usize, |
| mut fold: impl FnMut(Acc, (usize, T)) -> R, |
| ) -> impl FnMut(Acc, T) -> R { |
| move |acc, item| { |
| count -= 1; |
| fold(acc, (count, item)) |
| } |
| } |
| |
| let count = self.count + self.iter.len(); |
| self.iter.try_rfold(init, enumerate(count, fold)) |
| } |
| |
| #[inline] |
| fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc |
| where |
| Fold: FnMut(Acc, Self::Item) -> Acc, |
| { |
| // Can safely add and subtract the count, as `ExactSizeIterator` promises |
| // that the number of elements fits into a `usize`. |
| fn enumerate<T, Acc>( |
| mut count: usize, |
| mut fold: impl FnMut(Acc, (usize, T)) -> Acc, |
| ) -> impl FnMut(Acc, T) -> Acc { |
| move |acc, item| { |
| count -= 1; |
| fold(acc, (count, item)) |
| } |
| } |
| |
| let count = self.count + self.iter.len(); |
| self.iter.rfold(init, enumerate(count, fold)) |
| } |
| |
| #[inline] |
| fn advance_back_by(&mut self, n: usize) -> Result<(), usize> { |
| // we do not need to update the count since that only tallies the number of items |
| // consumed from the front. consuming items from the back can never reduce that. |
| self.iter.advance_back_by(n) |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<I> ExactSizeIterator for Enumerate<I> |
| where |
| I: ExactSizeIterator, |
| { |
| fn len(&self) -> usize { |
| self.iter.len() |
| } |
| |
| fn is_empty(&self) -> bool { |
| self.iter.is_empty() |
| } |
| } |
| |
| #[doc(hidden)] |
| #[unstable(feature = "trusted_random_access", issue = "none")] |
| unsafe impl<I> TrustedRandomAccess for Enumerate<I> where I: TrustedRandomAccess {} |
| |
| #[doc(hidden)] |
| #[unstable(feature = "trusted_random_access", issue = "none")] |
| unsafe impl<I> TrustedRandomAccessNoCoerce for Enumerate<I> |
| where |
| I: TrustedRandomAccessNoCoerce, |
| { |
| const MAY_HAVE_SIDE_EFFECT: bool = I::MAY_HAVE_SIDE_EFFECT; |
| } |
| |
| #[stable(feature = "fused", since = "1.26.0")] |
| impl<I> FusedIterator for Enumerate<I> where I: FusedIterator {} |
| |
| #[unstable(feature = "trusted_len", issue = "37572")] |
| unsafe impl<I> TrustedLen for Enumerate<I> where I: TrustedLen {} |
| |
| #[unstable(issue = "none", feature = "inplace_iteration")] |
| unsafe impl<I> SourceIter for Enumerate<I> |
| 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> InPlaceIterable for Enumerate<I> {} |