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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
commit | 698f8c2f01ea549d77d7dc3338a12e04c11057b9 (patch) | |
tree | 173a775858bd501c378080a10dca74132f05bc50 /library/core/src/iter/adapters/skip.rs | |
parent | Initial commit. (diff) | |
download | rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.tar.xz rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.zip |
Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'library/core/src/iter/adapters/skip.rs')
-rw-r--r-- | library/core/src/iter/adapters/skip.rs | 239 |
1 files changed, 239 insertions, 0 deletions
diff --git a/library/core/src/iter/adapters/skip.rs b/library/core/src/iter/adapters/skip.rs new file mode 100644 index 000000000..2c283100f --- /dev/null +++ b/library/core/src/iter/adapters/skip.rs @@ -0,0 +1,239 @@ +use crate::intrinsics::unlikely; +use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable}; +use crate::ops::{ControlFlow, Try}; + +/// An iterator that skips over `n` elements of `iter`. +/// +/// This `struct` is created by the [`skip`] method on [`Iterator`]. See its +/// documentation for more. +/// +/// [`skip`]: Iterator::skip +/// [`Iterator`]: trait.Iterator.html +#[derive(Clone, Debug)] +#[must_use = "iterators are lazy and do nothing unless consumed"] +#[stable(feature = "rust1", since = "1.0.0")] +pub struct Skip<I> { + iter: I, + n: usize, +} + +impl<I> Skip<I> { + pub(in crate::iter) fn new(iter: I, n: usize) -> Skip<I> { + Skip { iter, n } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<I> Iterator for Skip<I> +where + I: Iterator, +{ + type Item = <I as Iterator>::Item; + + #[inline] + fn next(&mut self) -> Option<I::Item> { + if unlikely(self.n > 0) { + self.iter.nth(crate::mem::take(&mut self.n) - 1)?; + } + self.iter.next() + } + + #[inline] + fn nth(&mut self, n: usize) -> Option<I::Item> { + // Can't just add n + self.n due to overflow. + if self.n > 0 { + let to_skip = self.n; + self.n = 0; + // nth(n) skips n+1 + self.iter.nth(to_skip - 1)?; + } + self.iter.nth(n) + } + + #[inline] + fn count(mut self) -> usize { + if self.n > 0 { + // nth(n) skips n+1 + if self.iter.nth(self.n - 1).is_none() { + return 0; + } + } + self.iter.count() + } + + #[inline] + fn last(mut self) -> Option<I::Item> { + if self.n > 0 { + // nth(n) skips n+1 + self.iter.nth(self.n - 1)?; + } + self.iter.last() + } + + #[inline] + fn size_hint(&self) -> (usize, Option<usize>) { + let (lower, upper) = self.iter.size_hint(); + + let lower = lower.saturating_sub(self.n); + let upper = match upper { + Some(x) => Some(x.saturating_sub(self.n)), + None => None, + }; + + (lower, upper) + } + + #[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>, + { + let n = self.n; + self.n = 0; + if n > 0 { + // nth(n) skips n+1 + if self.iter.nth(n - 1).is_none() { + return try { init }; + } + } + self.iter.try_fold(init, fold) + } + + #[inline] + fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc + where + Fold: FnMut(Acc, Self::Item) -> Acc, + { + if self.n > 0 { + // nth(n) skips n+1 + if self.iter.nth(self.n - 1).is_none() { + return init; + } + } + self.iter.fold(init, fold) + } + + #[inline] + #[rustc_inherit_overflow_checks] + fn advance_by(&mut self, n: usize) -> Result<(), usize> { + let mut rem = n; + let step_one = self.n.saturating_add(rem); + + match self.iter.advance_by(step_one) { + Ok(_) => { + rem -= step_one - self.n; + self.n = 0; + } + Err(advanced) => { + let advanced_without_skip = advanced.saturating_sub(self.n); + self.n = self.n.saturating_sub(advanced); + return if n == 0 { Ok(()) } else { Err(advanced_without_skip) }; + } + } + + // step_one calculation may have saturated + if unlikely(rem > 0) { + return match self.iter.advance_by(rem) { + ret @ Ok(_) => ret, + Err(advanced) => { + rem -= advanced; + Err(n - rem) + } + }; + } + + Ok(()) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<I> ExactSizeIterator for Skip<I> where I: ExactSizeIterator {} + +#[stable(feature = "double_ended_skip_iterator", since = "1.9.0")] +impl<I> DoubleEndedIterator for Skip<I> +where + I: DoubleEndedIterator + ExactSizeIterator, +{ + fn next_back(&mut self) -> Option<Self::Item> { + if self.len() > 0 { self.iter.next_back() } else { None } + } + + #[inline] + fn nth_back(&mut self, n: usize) -> Option<I::Item> { + let len = self.len(); + if n < len { + self.iter.nth_back(n) + } else { + if len > 0 { + // consume the original iterator + self.iter.nth_back(len - 1); + } + None + } + } + + fn try_rfold<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<T, Acc, R: Try<Output = Acc>>( + mut n: usize, + mut fold: impl FnMut(Acc, T) -> R, + ) -> impl FnMut(Acc, T) -> ControlFlow<R, Acc> { + move |acc, x| { + n -= 1; + let r = fold(acc, x); + if n == 0 { ControlFlow::Break(r) } else { ControlFlow::from_try(r) } + } + } + + let n = self.len(); + if n == 0 { try { init } } else { self.iter.try_rfold(init, check(n, fold)).into_try() } + } + + fn rfold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc + where + Fold: FnMut(Acc, Self::Item) -> Acc, + { + #[inline] + fn ok<Acc, T>(mut f: impl FnMut(Acc, T) -> Acc) -> impl FnMut(Acc, T) -> Result<Acc, !> { + move |acc, x| Ok(f(acc, x)) + } + + self.try_rfold(init, ok(fold)).unwrap() + } + + #[inline] + fn advance_back_by(&mut self, n: usize) -> Result<(), usize> { + let min = crate::cmp::min(self.len(), n); + return match self.iter.advance_back_by(min) { + ret @ Ok(_) if n <= min => ret, + Ok(_) => Err(min), + _ => panic!("ExactSizeIterator contract violation"), + }; + } +} + +#[stable(feature = "fused", since = "1.26.0")] +impl<I> FusedIterator for Skip<I> where I: FusedIterator {} + +#[unstable(issue = "none", feature = "inplace_iteration")] +unsafe impl<I> SourceIter for Skip<I> +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> InPlaceIterable for Skip<I> {} |