| use crate::fmt; |
| use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable}; |
| use crate::ops::{ControlFlow, Try}; |
| |
| /// An iterator that only accepts elements while `predicate` returns `true`. |
| /// |
| /// This `struct` is created by the [`take_while`] method on [`Iterator`]. See its |
| /// documentation for more. |
| /// |
| /// [`take_while`]: Iterator::take_while |
| /// [`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 TakeWhile<I, P> { |
| iter: I, |
| flag: bool, |
| predicate: P, |
| } |
| |
| impl<I, P> TakeWhile<I, P> { |
| pub(in crate::iter) fn new(iter: I, predicate: P) -> TakeWhile<I, P> { |
| TakeWhile { iter, flag: false, predicate } |
| } |
| } |
| |
| #[stable(feature = "core_impl_debug", since = "1.9.0")] |
| impl<I: fmt::Debug, P> fmt::Debug for TakeWhile<I, P> { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| f.debug_struct("TakeWhile").field("iter", &self.iter).field("flag", &self.flag).finish() |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<I: Iterator, P> Iterator for TakeWhile<I, P> |
| where |
| P: FnMut(&I::Item) -> bool, |
| { |
| type Item = I::Item; |
| |
| #[inline] |
| fn next(&mut self) -> Option<I::Item> { |
| if self.flag { |
| None |
| } else { |
| let x = self.iter.next()?; |
| if (self.predicate)(&x) { |
| Some(x) |
| } else { |
| self.flag = true; |
| None |
| } |
| } |
| } |
| |
| #[inline] |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| if self.flag { |
| (0, Some(0)) |
| } else { |
| 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, fold: Fold) -> R |
| where |
| Self: Sized, |
| Fold: FnMut(Acc, Self::Item) -> R, |
| R: Try<Output = Acc>, |
| { |
| fn check<'a, T, Acc, R: Try<Output = Acc>>( |
| flag: &'a mut bool, |
| p: &'a mut impl FnMut(&T) -> bool, |
| mut fold: impl FnMut(Acc, T) -> R + 'a, |
| ) -> impl FnMut(Acc, T) -> ControlFlow<R, Acc> + 'a { |
| move |acc, x| { |
| if p(&x) { |
| ControlFlow::from_try(fold(acc, x)) |
| } else { |
| *flag = true; |
| ControlFlow::Break(try { acc }) |
| } |
| } |
| } |
| |
| if self.flag { |
| try { init } |
| } else { |
| let flag = &mut self.flag; |
| let p = &mut self.predicate; |
| self.iter.try_fold(init, check(flag, p, fold)).into_try() |
| } |
| } |
| |
| impl_fold_via_try_fold! { fold -> try_fold } |
| } |
| |
| #[stable(feature = "fused", since = "1.26.0")] |
| impl<I, P> FusedIterator for TakeWhile<I, P> |
| where |
| I: FusedIterator, |
| P: FnMut(&I::Item) -> bool, |
| { |
| } |
| |
| #[unstable(issue = "none", feature = "inplace_iteration")] |
| unsafe impl<P, I> SourceIter for TakeWhile<I, P> |
| 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, F> InPlaceIterable for TakeWhile<I, F> where |
| F: FnMut(&I::Item) -> bool |
| { |
| } |