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Diffstat (limited to 'library/core/src/iter/adapters/skip_while.rs')
-rw-r--r-- | library/core/src/iter/adapters/skip_while.rs | 125 |
1 files changed, 125 insertions, 0 deletions
diff --git a/library/core/src/iter/adapters/skip_while.rs b/library/core/src/iter/adapters/skip_while.rs new file mode 100644 index 000000000..f29661779 --- /dev/null +++ b/library/core/src/iter/adapters/skip_while.rs @@ -0,0 +1,125 @@ +use crate::fmt; +use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable}; +use crate::ops::Try; + +/// An iterator that rejects elements while `predicate` returns `true`. +/// +/// This `struct` is created by the [`skip_while`] method on [`Iterator`]. See its +/// documentation for more. +/// +/// [`skip_while`]: Iterator::skip_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 SkipWhile<I, P> { + iter: I, + flag: bool, + predicate: P, +} + +impl<I, P> SkipWhile<I, P> { + pub(in crate::iter) fn new(iter: I, predicate: P) -> SkipWhile<I, P> { + SkipWhile { iter, flag: false, predicate } + } +} + +#[stable(feature = "core_impl_debug", since = "1.9.0")] +impl<I: fmt::Debug, P> fmt::Debug for SkipWhile<I, P> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_struct("SkipWhile").field("iter", &self.iter).field("flag", &self.flag).finish() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<I: Iterator, P> Iterator for SkipWhile<I, P> +where + P: FnMut(&I::Item) -> bool, +{ + type Item = I::Item; + + #[inline] + fn next(&mut self) -> Option<I::Item> { + fn check<'a, T>( + flag: &'a mut bool, + pred: &'a mut impl FnMut(&T) -> bool, + ) -> impl FnMut(&T) -> bool + 'a { + move |x| { + if *flag || !pred(x) { + *flag = true; + true + } else { + false + } + } + } + + let flag = &mut self.flag; + let pred = &mut self.predicate; + self.iter.find(check(flag, pred)) + } + + #[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, mut init: Acc, mut fold: Fold) -> R + where + Self: Sized, + Fold: FnMut(Acc, Self::Item) -> R, + R: Try<Output = Acc>, + { + if !self.flag { + match self.next() { + Some(v) => init = fold(init, v)?, + None => return try { init }, + } + } + self.iter.try_fold(init, fold) + } + + #[inline] + fn fold<Acc, Fold>(mut self, mut init: Acc, mut fold: Fold) -> Acc + where + Fold: FnMut(Acc, Self::Item) -> Acc, + { + if !self.flag { + match self.next() { + Some(v) => init = fold(init, v), + None => return init, + } + } + self.iter.fold(init, fold) + } +} + +#[stable(feature = "fused", since = "1.26.0")] +impl<I, P> FusedIterator for SkipWhile<I, P> +where + I: FusedIterator, + P: FnMut(&I::Item) -> bool, +{ +} + +#[unstable(issue = "none", feature = "inplace_iteration")] +unsafe impl<P, I> SourceIter for SkipWhile<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 SkipWhile<I, F> where + F: FnMut(&I::Item) -> bool +{ +} |