| use crate::fmt; |
| use crate::iter::{adapters::SourceIter, InPlaceIterable}; |
| use crate::ops::{ControlFlow, Try}; |
| |
| /// An iterator that only accepts elements while `predicate` returns `Some(_)`. |
| /// |
| /// This `struct` is created by the [`map_while`] method on [`Iterator`]. See its |
| /// documentation for more. |
| /// |
| /// [`map_while`]: Iterator::map_while |
| /// [`Iterator`]: trait.Iterator.html |
| #[must_use = "iterators are lazy and do nothing unless consumed"] |
| #[unstable(feature = "iter_map_while", reason = "recently added", issue = "68537")] |
| #[derive(Clone)] |
| pub struct MapWhile<I, P> { |
| iter: I, |
| predicate: P, |
| } |
| |
| impl<I, P> MapWhile<I, P> { |
| pub(in crate::iter) fn new(iter: I, predicate: P) -> MapWhile<I, P> { |
| MapWhile { iter, predicate } |
| } |
| } |
| |
| #[unstable(feature = "iter_map_while", reason = "recently added", issue = "68537")] |
| impl<I: fmt::Debug, P> fmt::Debug for MapWhile<I, P> { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| f.debug_struct("MapWhile").field("iter", &self.iter).finish() |
| } |
| } |
| |
| #[unstable(feature = "iter_map_while", reason = "recently added", issue = "68537")] |
| impl<B, I: Iterator, P> Iterator for MapWhile<I, P> |
| where |
| P: FnMut(I::Item) -> Option<B>, |
| { |
| type Item = B; |
| |
| #[inline] |
| fn next(&mut self) -> Option<B> { |
| let x = self.iter.next()?; |
| (self.predicate)(x) |
| } |
| |
| #[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 predicate |
| } |
| |
| #[inline] |
| fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R |
| where |
| Self: Sized, |
| Fold: FnMut(Acc, Self::Item) -> R, |
| R: Try<Output = Acc>, |
| { |
| let Self { iter, predicate } = self; |
| iter.try_fold(init, |acc, x| match predicate(x) { |
| Some(item) => ControlFlow::from_try(fold(acc, item)), |
| None => ControlFlow::Break(try { acc }), |
| }) |
| .into_try() |
| } |
| |
| #[inline] |
| fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc |
| where |
| Self: Sized, |
| Fold: FnMut(Acc, Self::Item) -> Acc, |
| { |
| #[inline] |
| fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> { |
| move |acc, x| Ok(f(acc, x)) |
| } |
| |
| self.try_fold(init, ok(fold)).unwrap() |
| } |
| } |
| |
| #[unstable(issue = "none", feature = "inplace_iteration")] |
| unsafe impl<S: Iterator, B, I: Iterator, P> SourceIter for MapWhile<I, P> |
| where |
| P: FnMut(I::Item) -> Option<B>, |
| I: SourceIter<Source = S>, |
| { |
| type Source = S; |
| |
| #[inline] |
| unsafe fn as_inner(&mut self) -> &mut S { |
| // 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<B, I: InPlaceIterable, P> InPlaceIterable for MapWhile<I, P> where |
| P: FnMut(I::Item) -> Option<B> |
| { |
| } |