diff options
Diffstat (limited to 'library/core/src/iter/adapters/take_while.rs')
-rw-r--r-- | library/core/src/iter/adapters/take_while.rs | 138 |
1 files changed, 138 insertions, 0 deletions
diff --git a/library/core/src/iter/adapters/take_while.rs b/library/core/src/iter/adapters/take_while.rs new file mode 100644 index 000000000..ded216da9 --- /dev/null +++ b/library/core/src/iter/adapters/take_while.rs @@ -0,0 +1,138 @@ +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() + } + } + + #[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() + } +} + +#[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 +{ +} |