| use crate::fmt; |
| use crate::iter::{adapters::SourceIter, InPlaceIterable}; |
| use crate::ops::{ControlFlow, Try}; |
| |
| /// An iterator to maintain state while iterating another iterator. |
| /// |
| /// This `struct` is created by the [`scan`] method on [`Iterator`]. See its |
| /// documentation for more. |
| /// |
| /// [`scan`]: Iterator::scan |
| /// [`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 Scan<I, St, F> { |
| iter: I, |
| f: F, |
| state: St, |
| } |
| |
| impl<I, St, F> Scan<I, St, F> { |
| pub(in crate::iter) fn new(iter: I, state: St, f: F) -> Scan<I, St, F> { |
| Scan { iter, state, f } |
| } |
| } |
| |
| #[stable(feature = "core_impl_debug", since = "1.9.0")] |
| impl<I: fmt::Debug, St: fmt::Debug, F> fmt::Debug for Scan<I, St, F> { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| f.debug_struct("Scan").field("iter", &self.iter).field("state", &self.state).finish() |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<B, I, St, F> Iterator for Scan<I, St, F> |
| where |
| I: Iterator, |
| F: FnMut(&mut St, I::Item) -> Option<B>, |
| { |
| type Item = B; |
| |
| #[inline] |
| fn next(&mut self) -> Option<B> { |
| let a = self.iter.next()?; |
| (self.f)(&mut self.state, a) |
| } |
| |
| #[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 scan function |
| } |
| |
| #[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>, |
| { |
| fn scan<'a, T, St, B, Acc, R: Try<Output = Acc>>( |
| state: &'a mut St, |
| f: &'a mut impl FnMut(&mut St, T) -> Option<B>, |
| mut fold: impl FnMut(Acc, B) -> R + 'a, |
| ) -> impl FnMut(Acc, T) -> ControlFlow<R, Acc> + 'a { |
| move |acc, x| match f(state, x) { |
| None => ControlFlow::Break(try { acc }), |
| Some(x) => ControlFlow::from_try(fold(acc, x)), |
| } |
| } |
| |
| let state = &mut self.state; |
| let f = &mut self.f; |
| self.iter.try_fold(init, scan(state, f, fold)).into_try() |
| } |
| |
| impl_fold_via_try_fold! { fold -> try_fold } |
| } |
| |
| #[unstable(issue = "none", feature = "inplace_iteration")] |
| unsafe impl<St, F, I> SourceIter for Scan<I, St, F> |
| 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<St, F, B, I: InPlaceIterable> InPlaceIterable for Scan<I, St, F> where |
| F: FnMut(&mut St, I::Item) -> Option<B> |
| { |
| } |