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Diffstat (limited to '')
-rw-r--r-- | library/core/src/iter/adapters/map_while.rs | 100 |
1 files changed, 100 insertions, 0 deletions
diff --git a/library/core/src/iter/adapters/map_while.rs b/library/core/src/iter/adapters/map_while.rs new file mode 100644 index 000000000..1e8d6bf3e --- /dev/null +++ b/library/core/src/iter/adapters/map_while.rs @@ -0,0 +1,100 @@ +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"] +#[stable(feature = "iter_map_while", since = "1.57.0")] +#[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 } + } +} + +#[stable(feature = "iter_map_while", since = "1.57.0")] +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() + } +} + +#[stable(feature = "iter_map_while", since = "1.57.0")] +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<I, P> SourceIter for MapWhile<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<B, I: InPlaceIterable, P> InPlaceIterable for MapWhile<I, P> where + P: FnMut(I::Item) -> Option<B> +{ +} |