use crate::intrinsics::unlikely;
use crate::iter::adapters::zip::try_get_unchecked;
use crate::iter::TrustedFused;
use crate::iter::{
adapters::SourceIter, FusedIterator, InPlaceIterable, TrustedLen, TrustedRandomAccess,
TrustedRandomAccessNoCoerce,
};
use crate::num::NonZeroUsize;
use crate::ops::{ControlFlow, Try};
#[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))
} else {
self.iter.next()
}
}
#[inline]
fn nth(&mut self, n: usize) -> Option<I::Item> {
if self.n > 0 {
let skip: usize = crate::mem::take(&mut self.n);
let n = match skip.checked_add(n) {
Some(nth) => nth,
None => {
self.iter.nth(skip - 1)?;
n
}
};
self.iter.nth(n)
} else {
self.iter.nth(n)
}
}
#[inline]
fn count(mut self) -> usize {
if self.n > 0 {
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 {
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 {
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 {
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, mut n: usize) -> Result<(), NonZeroUsize> {
let skip_inner = self.n;
let skip_and_advance = skip_inner.saturating_add(n);
let remainder = match self.iter.advance_by(skip_and_advance) {
Ok(()) => 0,
Err(n) => n.get(),
};
let advanced_inner = skip_and_advance - remainder;
n -= advanced_inner.saturating_sub(skip_inner);
self.n = self.n.saturating_sub(advanced_inner);
if unlikely(remainder == 0 && n > 0) {
n = match self.iter.advance_by(n) {
Ok(()) => 0,
Err(n) => n.get(),
}
}
NonZeroUsize::new(n).map_or(Ok(()), Err)
}
#[doc(hidden)]
unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item
where
Self: TrustedRandomAccessNoCoerce,
{
unsafe {
if Self::MAY_HAVE_SIDE_EFFECT && idx == 0 {
for skipped_idx in 0..self.n {
drop(try_get_unchecked(&mut self.iter, skipped_idx));
}
}
try_get_unchecked(&mut self.iter, idx + self.n)
}
}
}
#[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 {
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() }
}
impl_fold_via_try_fold! { rfold -> try_rfold }
#[inline]
fn advance_back_by(&mut self, n: usize) -> Result<(), NonZeroUsize> {
let min = crate::cmp::min(self.len(), n);
let rem = self.iter.advance_back_by(min);
assert!(rem.is_ok(), "ExactSizeIterator contract violation");
NonZeroUsize::new(n - min).map_or(Ok(()), Err)
}
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I> FusedIterator for Skip<I> where I: FusedIterator {}
#[unstable(issue = "none", feature = "trusted_fused")]
unsafe impl<I: TrustedFused> TrustedFused for Skip<I> {}
#[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 {
unsafe { SourceIter::as_inner(&mut self.iter) }
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<I: InPlaceIterable> InPlaceIterable for Skip<I> {
const EXPAND_BY: Option<NonZeroUsize> = I::EXPAND_BY;
const MERGE_BY: Option<NonZeroUsize> = I::MERGE_BY;
}
#[doc(hidden)]
#[unstable(feature = "trusted_random_access", issue = "none")]
unsafe impl<I> TrustedRandomAccess for Skip<I> where I: TrustedRandomAccess {}
#[doc(hidden)]
#[unstable(feature = "trusted_random_access", issue = "none")]
unsafe impl<I> TrustedRandomAccessNoCoerce for Skip<I>
where
I: TrustedRandomAccessNoCoerce,
{
const MAY_HAVE_SIDE_EFFECT: bool = I::MAY_HAVE_SIDE_EFFECT;
}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<I> TrustedLen for Skip<I> where I: Iterator + TrustedRandomAccess {}