use cmp;
use fmt;
use ops::Try;
use usize;
use intrinsics;
use super::{Iterator, DoubleEndedIterator, ExactSizeIterator, FusedIterator, TrustedLen};
use super::LoopState;
mod chain;
mod flatten;
mod zip;
pub use self::chain::Chain;
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::flatten::{FlatMap, Flatten};
pub use self::zip::Zip;
pub(crate) use self::zip::TrustedRandomAccess;
#[derive(Clone, Debug)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Rev<T> {
    iter: T
}
impl<T> Rev<T> {
    pub(super) fn new(iter: T) -> Rev<T> {
        Rev { iter }
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> Iterator for Rev<I> where I: DoubleEndedIterator {
    type Item = <I as Iterator>::Item;
    #[inline]
    fn next(&mut self) -> Option<<I as Iterator>::Item> { self.iter.next_back() }
    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) { self.iter.size_hint() }
    #[inline]
    fn nth(&mut self, n: usize) -> Option<<I as Iterator>::Item> { self.iter.nth_back(n) }
    fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R where
        Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
    {
        self.iter.try_rfold(init, f)
    }
    fn fold<Acc, F>(self, init: Acc, f: F) -> Acc
        where F: FnMut(Acc, Self::Item) -> Acc,
    {
        self.iter.rfold(init, f)
    }
    #[inline]
    fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
        where P: FnMut(&Self::Item) -> bool
    {
        self.iter.rfind(predicate)
    }
    #[inline]
    fn rposition<P>(&mut self, predicate: P) -> Option<usize> where
        P: FnMut(Self::Item) -> bool
    {
        self.iter.position(predicate)
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> DoubleEndedIterator for Rev<I> where I: DoubleEndedIterator {
    #[inline]
    fn next_back(&mut self) -> Option<<I as Iterator>::Item> { self.iter.next() }
    #[inline]
    fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item> { self.iter.nth(n) }
    fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
        Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
    {
        self.iter.try_fold(init, f)
    }
    fn rfold<Acc, F>(self, init: Acc, f: F) -> Acc
        where F: FnMut(Acc, Self::Item) -> Acc,
    {
        self.iter.fold(init, f)
    }
    fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item>
        where P: FnMut(&Self::Item) -> bool
    {
        self.iter.find(predicate)
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> ExactSizeIterator for Rev<I>
    where I: ExactSizeIterator + DoubleEndedIterator
{
    fn len(&self) -> usize {
        self.iter.len()
    }
    fn is_empty(&self) -> bool {
        self.iter.is_empty()
    }
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I> FusedIterator for Rev<I>
    where I: FusedIterator + DoubleEndedIterator {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<I> TrustedLen for Rev<I>
    where I: TrustedLen + DoubleEndedIterator {}
#[unstable(feature = "iter_copied", issue = "57127")]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[derive(Clone, Debug)]
pub struct Copied<I> {
    it: I,
}
impl<I> Copied<I> {
    pub(super) fn new(it: I) -> Copied<I> {
        Copied { it }
    }
}
#[unstable(feature = "iter_copied", issue = "57127")]
impl<'a, I, T: 'a> Iterator for Copied<I>
    where I: Iterator<Item=&'a T>, T: Copy
{
    type Item = T;
    fn next(&mut self) -> Option<T> {
        self.it.next().copied()
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.it.size_hint()
    }
    fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R where
        Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
    {
        self.it.try_fold(init, move |acc, &elt| f(acc, elt))
    }
    fn fold<Acc, F>(self, init: Acc, mut f: F) -> Acc
        where F: FnMut(Acc, Self::Item) -> Acc,
    {
        self.it.fold(init, move |acc, &elt| f(acc, elt))
    }
}
#[unstable(feature = "iter_copied", issue = "57127")]
impl<'a, I, T: 'a> DoubleEndedIterator for Copied<I>
    where I: DoubleEndedIterator<Item=&'a T>, T: Copy
{
    fn next_back(&mut self) -> Option<T> {
        self.it.next_back().copied()
    }
    fn try_rfold<B, F, R>(&mut self, init: B, mut f: F) -> R where
        Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
    {
        self.it.try_rfold(init, move |acc, &elt| f(acc, elt))
    }
    fn rfold<Acc, F>(self, init: Acc, mut f: F) -> Acc
        where F: FnMut(Acc, Self::Item) -> Acc,
    {
        self.it.rfold(init, move |acc, &elt| f(acc, elt))
    }
}
#[unstable(feature = "iter_copied", issue = "57127")]
impl<'a, I, T: 'a> ExactSizeIterator for Copied<I>
    where I: ExactSizeIterator<Item=&'a T>, T: Copy
{
    fn len(&self) -> usize {
        self.it.len()
    }
    fn is_empty(&self) -> bool {
        self.it.is_empty()
    }
}
#[unstable(feature = "iter_copied", issue = "57127")]
impl<'a, I, T: 'a> FusedIterator for Copied<I>
    where I: FusedIterator<Item=&'a T>, T: Copy
{}
#[doc(hidden)]
unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Copied<I>
    where I: TrustedRandomAccess<Item=&'a T>, T: Copy
{
    unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
        *self.it.get_unchecked(i)
    }
    #[inline]
    fn may_have_side_effect() -> bool {
        I::may_have_side_effect()
    }
}
#[unstable(feature = "iter_copied", issue = "57127")]
unsafe impl<'a, I, T: 'a> TrustedLen for Copied<I>
    where I: TrustedLen<Item=&'a T>,
          T: Copy
{}
#[stable(feature = "iter_cloned", since = "1.1.0")]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[derive(Clone, Debug)]
pub struct Cloned<I> {
    it: I,
}
impl<I> Cloned<I> {
    pub(super) fn new(it: I) -> Cloned<I> {
        Cloned { it }
    }
}
#[stable(feature = "iter_cloned", since = "1.1.0")]
impl<'a, I, T: 'a> Iterator for Cloned<I>
    where I: Iterator<Item=&'a T>, T: Clone
{
    type Item = T;
    fn next(&mut self) -> Option<T> {
        self.it.next().cloned()
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.it.size_hint()
    }
    fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R where
        Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
    {
        self.it.try_fold(init, move |acc, elt| f(acc, elt.clone()))
    }
    fn fold<Acc, F>(self, init: Acc, mut f: F) -> Acc
        where F: FnMut(Acc, Self::Item) -> Acc,
    {
        self.it.fold(init, move |acc, elt| f(acc, elt.clone()))
    }
}
#[stable(feature = "iter_cloned", since = "1.1.0")]
impl<'a, I, T: 'a> DoubleEndedIterator for Cloned<I>
    where I: DoubleEndedIterator<Item=&'a T>, T: Clone
{
    fn next_back(&mut self) -> Option<T> {
        self.it.next_back().cloned()
    }
    fn try_rfold<B, F, R>(&mut self, init: B, mut f: F) -> R where
        Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
    {
        self.it.try_rfold(init, move |acc, elt| f(acc, elt.clone()))
    }
    fn rfold<Acc, F>(self, init: Acc, mut f: F) -> Acc
        where F: FnMut(Acc, Self::Item) -> Acc,
    {
        self.it.rfold(init, move |acc, elt| f(acc, elt.clone()))
    }
}
#[stable(feature = "iter_cloned", since = "1.1.0")]
impl<'a, I, T: 'a> ExactSizeIterator for Cloned<I>
    where I: ExactSizeIterator<Item=&'a T>, T: Clone
{
    fn len(&self) -> usize {
        self.it.len()
    }
    fn is_empty(&self) -> bool {
        self.it.is_empty()
    }
}
#[stable(feature = "fused", since = "1.26.0")]
impl<'a, I, T: 'a> FusedIterator for Cloned<I>
    where I: FusedIterator<Item=&'a T>, T: Clone
{}
#[doc(hidden)]
unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Cloned<I>
    where I: TrustedRandomAccess<Item=&'a T>, T: Clone
{
    default unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
        self.it.get_unchecked(i).clone()
    }
    #[inline]
    default fn may_have_side_effect() -> bool { true }
}
#[doc(hidden)]
unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Cloned<I>
    where I: TrustedRandomAccess<Item=&'a T>, T: Copy
{
    unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
        *self.it.get_unchecked(i)
    }
    #[inline]
    fn may_have_side_effect() -> bool {
        I::may_have_side_effect()
    }
}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<'a, I, T: 'a> TrustedLen for Cloned<I>
    where I: TrustedLen<Item=&'a T>,
          T: Clone
{}
#[derive(Clone, Debug)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Cycle<I> {
    orig: I,
    iter: I,
}
impl<I: Clone> Cycle<I> {
    pub(super) fn new(iter: I) -> Cycle<I> {
        Cycle { orig: iter.clone(), iter }
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> Iterator for Cycle<I> where I: Clone + Iterator {
    type Item = <I as Iterator>::Item;
    #[inline]
    fn next(&mut self) -> Option<<I as Iterator>::Item> {
        match self.iter.next() {
            None => { self.iter = self.orig.clone(); self.iter.next() }
            y => y
        }
    }
    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        
        match self.orig.size_hint() {
            sz @ (0, Some(0)) => sz,
            (0, _) => (0, None),
            _ => (usize::MAX, None)
        }
    }
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I> FusedIterator for Cycle<I> where I: Clone + Iterator {}
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "iterator_step_by", since = "1.28.0")]
#[derive(Clone, Debug)]
pub struct StepBy<I> {
    iter: I,
    step: usize,
    first_take: bool,
}
impl<I> StepBy<I> {
    pub(super) fn new(iter: I, step: usize) -> StepBy<I> {
        assert!(step != 0);
        StepBy { iter, step: step - 1, first_take: true }
    }
}
#[stable(feature = "iterator_step_by", since = "1.28.0")]
impl<I> Iterator for StepBy<I> where I: Iterator {
    type Item = I::Item;
    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        if self.first_take {
            self.first_take = false;
            self.iter.next()
        } else {
            self.iter.nth(self.step)
        }
    }
    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let inner_hint = self.iter.size_hint();
        if self.first_take {
            let f = |n| if n == 0 { 0 } else { 1 + (n-1)/(self.step+1) };
            (f(inner_hint.0), inner_hint.1.map(f))
        } else {
            let f = |n| n / (self.step+1);
            (f(inner_hint.0), inner_hint.1.map(f))
        }
    }
    #[inline]
    fn nth(&mut self, mut n: usize) -> Option<Self::Item> {
        if self.first_take {
            self.first_take = false;
            let first = self.iter.next();
            if n == 0 {
                return first;
            }
            n -= 1;
        }
        
        
        
        let mut step = self.step + 1;
        
        
        if n == usize::MAX {
            self.iter.nth(step - 1);
        } else {
            n += 1;
        }
        
        loop {
            let mul = n.checked_mul(step);
            if unsafe { intrinsics::likely(mul.is_some()) } {
                return self.iter.nth(mul.unwrap() - 1);
            }
            let div_n = usize::MAX / n;
            let div_step = usize::MAX / step;
            let nth_n = div_n * n;
            let nth_step = div_step * step;
            let nth = if nth_n > nth_step {
                step -= div_n;
                nth_n
            } else {
                n -= div_step;
                nth_step
            };
            self.iter.nth(nth - 1);
        }
    }
}
#[stable(feature = "iterator_step_by", since = "1.28.0")]
impl<I> ExactSizeIterator for StepBy<I> where I: ExactSizeIterator {}
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct Map<I, F> {
    iter: I,
    f: F,
}
impl<I, F> Map<I, F> {
    pub(super) fn new(iter: I, f: F) -> Map<I, F> {
        Map { iter, f }
    }
}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<I: fmt::Debug, F> fmt::Debug for Map<I, F> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Map")
            .field("iter", &self.iter)
            .finish()
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I: Iterator, F> Iterator for Map<I, F> where F: FnMut(I::Item) -> B {
    type Item = B;
    #[inline]
    fn next(&mut self) -> Option<B> {
        self.iter.next().map(&mut self.f)
    }
    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
    fn try_fold<Acc, G, R>(&mut self, init: Acc, mut g: G) -> R where
        Self: Sized, G: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
    {
        let f = &mut self.f;
        self.iter.try_fold(init, move |acc, elt| g(acc, f(elt)))
    }
    fn fold<Acc, G>(self, init: Acc, mut g: G) -> Acc
        where G: FnMut(Acc, Self::Item) -> Acc,
    {
        let mut f = self.f;
        self.iter.fold(init, move |acc, elt| g(acc, f(elt)))
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for Map<I, F> where
    F: FnMut(I::Item) -> B,
{
    #[inline]
    fn next_back(&mut self) -> Option<B> {
        self.iter.next_back().map(&mut self.f)
    }
    fn try_rfold<Acc, G, R>(&mut self, init: Acc, mut g: G) -> R where
        Self: Sized, G: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
    {
        let f = &mut self.f;
        self.iter.try_rfold(init, move |acc, elt| g(acc, f(elt)))
    }
    fn rfold<Acc, G>(self, init: Acc, mut g: G) -> Acc
        where G: FnMut(Acc, Self::Item) -> Acc,
    {
        let mut f = self.f;
        self.iter.rfold(init, move |acc, elt| g(acc, f(elt)))
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I: ExactSizeIterator, F> ExactSizeIterator for Map<I, F>
    where F: FnMut(I::Item) -> B
{
    fn len(&self) -> usize {
        self.iter.len()
    }
    fn is_empty(&self) -> bool {
        self.iter.is_empty()
    }
}
#[stable(feature = "fused", since = "1.26.0")]
impl<B, I: FusedIterator, F> FusedIterator for Map<I, F>
    where F: FnMut(I::Item) -> B {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<B, I, F> TrustedLen for Map<I, F>
    where I: TrustedLen,
          F: FnMut(I::Item) -> B {}
#[doc(hidden)]
unsafe impl<B, I, F> TrustedRandomAccess for Map<I, F>
    where I: TrustedRandomAccess,
          F: FnMut(I::Item) -> B,
{
    unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
        (self.f)(self.iter.get_unchecked(i))
    }
    #[inline]
    fn may_have_side_effect() -> bool { true }
}
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct Filter<I, P> {
    iter: I,
    predicate: P,
}
impl<I, P> Filter<I, P> {
    pub(super) fn new(iter: I, predicate: P) -> Filter<I, P> {
        Filter { iter, predicate }
    }
}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<I: fmt::Debug, P> fmt::Debug for Filter<I, P> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Filter")
            .field("iter", &self.iter)
            .finish()
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator, P> Iterator for Filter<I, P> where P: FnMut(&I::Item) -> bool {
    type Item = I::Item;
    #[inline]
    fn next(&mut self) -> Option<I::Item> {
        for x in &mut self.iter {
            if (self.predicate)(&x) {
                return Some(x);
            }
        }
        None
    }
    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let (_, upper) = self.iter.size_hint();
        (0, upper) 
    }
    
    
    
    
    
    
    
    
    
    
    
    #[inline]
    fn count(mut self) -> usize {
        let mut count = 0;
        for x in &mut self.iter {
            count += (self.predicate)(&x) as usize;
        }
        count
    }
    #[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<Ok=Acc>
    {
        let predicate = &mut self.predicate;
        self.iter.try_fold(init, move |acc, item| if predicate(&item) {
            fold(acc, item)
        } else {
            Try::from_ok(acc)
        })
    }
    #[inline]
    fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        let mut predicate = self.predicate;
        self.iter.fold(init, move |acc, item| if predicate(&item) {
            fold(acc, item)
        } else {
            acc
        })
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: DoubleEndedIterator, P> DoubleEndedIterator for Filter<I, P>
    where P: FnMut(&I::Item) -> bool,
{
    #[inline]
    fn next_back(&mut self) -> Option<I::Item> {
        for x in self.iter.by_ref().rev() {
            if (self.predicate)(&x) {
                return Some(x);
            }
        }
        None
    }
    #[inline]
    fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
        Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
    {
        let predicate = &mut self.predicate;
        self.iter.try_rfold(init, move |acc, item| if predicate(&item) {
            fold(acc, item)
        } else {
            Try::from_ok(acc)
        })
    }
    #[inline]
    fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        let mut predicate = self.predicate;
        self.iter.rfold(init, move |acc, item| if predicate(&item) {
            fold(acc, item)
        } else {
            acc
        })
    }
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I: FusedIterator, P> FusedIterator for Filter<I, P>
    where P: FnMut(&I::Item) -> bool {}
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct FilterMap<I, F> {
    iter: I,
    f: F,
}
impl<I, F> FilterMap<I, F> {
    pub(super) fn new(iter: I, f: F) -> FilterMap<I, F> {
        FilterMap { iter, f }
    }
}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<I: fmt::Debug, F> fmt::Debug for FilterMap<I, F> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("FilterMap")
            .field("iter", &self.iter)
            .finish()
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I: Iterator, F> Iterator for FilterMap<I, F>
    where F: FnMut(I::Item) -> Option<B>,
{
    type Item = B;
    #[inline]
    fn next(&mut self) -> Option<B> {
        for x in self.iter.by_ref() {
            if let Some(y) = (self.f)(x) {
                return Some(y);
            }
        }
        None
    }
    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let (_, upper) = self.iter.size_hint();
        (0, upper) 
    }
    #[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<Ok=Acc>
    {
        let f = &mut self.f;
        self.iter.try_fold(init, move |acc, item| match f(item) {
            Some(x) => fold(acc, x),
            None => Try::from_ok(acc),
        })
    }
    #[inline]
    fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        let mut f = self.f;
        self.iter.fold(init, move |acc, item| match f(item) {
            Some(x) => fold(acc, x),
            None => acc,
        })
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for FilterMap<I, F>
    where F: FnMut(I::Item) -> Option<B>,
{
    #[inline]
    fn next_back(&mut self) -> Option<B> {
        for x in self.iter.by_ref().rev() {
            if let Some(y) = (self.f)(x) {
                return Some(y);
            }
        }
        None
    }
    #[inline]
    fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
        Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
    {
        let f = &mut self.f;
        self.iter.try_rfold(init, move |acc, item| match f(item) {
            Some(x) => fold(acc, x),
            None => Try::from_ok(acc),
        })
    }
    #[inline]
    fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        let mut f = self.f;
        self.iter.rfold(init, move |acc, item| match f(item) {
            Some(x) => fold(acc, x),
            None => acc,
        })
    }
}
#[stable(feature = "fused", since = "1.26.0")]
impl<B, I: FusedIterator, F> FusedIterator for FilterMap<I, F>
    where F: FnMut(I::Item) -> Option<B> {}
#[derive(Clone, Debug)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Enumerate<I> {
    iter: I,
    count: usize,
}
impl<I> Enumerate<I> {
    pub(super) fn new(iter: I) -> Enumerate<I> {
        Enumerate { iter, count: 0 }
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> Iterator for Enumerate<I> where I: Iterator {
    type Item = (usize, <I as Iterator>::Item);
    
    
    
    
    
    
    
    
    
    #[inline]
    #[rustc_inherit_overflow_checks]
    fn next(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
        self.iter.next().map(|a| {
            let ret = (self.count, a);
            
            self.count += 1;
            ret
        })
    }
    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
    #[inline]
    #[rustc_inherit_overflow_checks]
    fn nth(&mut self, n: usize) -> Option<(usize, I::Item)> {
        self.iter.nth(n).map(|a| {
            let i = self.count + n;
            self.count = i + 1;
            (i, a)
        })
    }
    #[inline]
    fn count(self) -> usize {
        self.iter.count()
    }
    #[inline]
    #[rustc_inherit_overflow_checks]
    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<Ok=Acc>
    {
        let count = &mut self.count;
        self.iter.try_fold(init, move |acc, item| {
            let acc = fold(acc, (*count, item));
            *count += 1;
            acc
        })
    }
    #[inline]
    #[rustc_inherit_overflow_checks]
    fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        let mut count = self.count;
        self.iter.fold(init, move |acc, item| {
            let acc = fold(acc, (count, item));
            count += 1;
            acc
        })
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> DoubleEndedIterator for Enumerate<I> where
    I: ExactSizeIterator + DoubleEndedIterator
{
    #[inline]
    fn next_back(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
        self.iter.next_back().map(|a| {
            let len = self.iter.len();
            
            
            (self.count + len, a)
        })
    }
    #[inline]
    fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
        Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
    {
        
        
        let mut count = self.count + self.iter.len();
        self.iter.try_rfold(init, move |acc, item| {
            count -= 1;
            fold(acc, (count, item))
        })
    }
    #[inline]
    fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        
        
        let mut count = self.count + self.iter.len();
        self.iter.rfold(init, move |acc, item| {
            count -= 1;
            fold(acc, (count, item))
        })
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> ExactSizeIterator for Enumerate<I> where I: ExactSizeIterator {
    fn len(&self) -> usize {
        self.iter.len()
    }
    fn is_empty(&self) -> bool {
        self.iter.is_empty()
    }
}
#[doc(hidden)]
unsafe impl<I> TrustedRandomAccess for Enumerate<I>
    where I: TrustedRandomAccess
{
    unsafe fn get_unchecked(&mut self, i: usize) -> (usize, I::Item) {
        (self.count + i, self.iter.get_unchecked(i))
    }
    fn may_have_side_effect() -> bool {
        I::may_have_side_effect()
    }
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I> FusedIterator for Enumerate<I> where I: FusedIterator {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<I> TrustedLen for Enumerate<I>
    where I: TrustedLen,
{}
#[derive(Clone, Debug)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Peekable<I: Iterator> {
    iter: I,
    
    peeked: Option<Option<I::Item>>,
}
impl<I: Iterator> Peekable<I> {
    pub(super) fn new(iter: I) -> Peekable<I> {
        Peekable { iter, peeked: None }
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator> Iterator for Peekable<I> {
    type Item = I::Item;
    #[inline]
    fn next(&mut self) -> Option<I::Item> {
        match self.peeked.take() {
            Some(v) => v,
            None => self.iter.next(),
        }
    }
    #[inline]
    #[rustc_inherit_overflow_checks]
    fn count(mut self) -> usize {
        match self.peeked.take() {
            Some(None) => 0,
            Some(Some(_)) => 1 + self.iter.count(),
            None => self.iter.count(),
        }
    }
    #[inline]
    fn nth(&mut self, n: usize) -> Option<I::Item> {
        match self.peeked.take() {
            Some(None) => None,
            Some(v @ Some(_)) if n == 0 => v,
            Some(Some(_)) => self.iter.nth(n - 1),
            None => self.iter.nth(n),
        }
    }
    #[inline]
    fn last(mut self) -> Option<I::Item> {
        let peek_opt = match self.peeked.take() {
            Some(None) => return None,
            Some(v) => v,
            None => None,
        };
        self.iter.last().or(peek_opt)
    }
    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let peek_len = match self.peeked {
            Some(None) => return (0, Some(0)),
            Some(Some(_)) => 1,
            None => 0,
        };
        let (lo, hi) = self.iter.size_hint();
        let lo = lo.saturating_add(peek_len);
        let hi = hi.and_then(|x| x.checked_add(peek_len));
        (lo, hi)
    }
    #[inline]
    fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R where
        Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
    {
        let acc = match self.peeked.take() {
            Some(None) => return Try::from_ok(init),
            Some(Some(v)) => f(init, v)?,
            None => init,
        };
        self.iter.try_fold(acc, f)
    }
    #[inline]
    fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        let acc = match self.peeked {
            Some(None) => return init,
            Some(Some(v)) => fold(init, v),
            None => init,
        };
        self.iter.fold(acc, fold)
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: ExactSizeIterator> ExactSizeIterator for Peekable<I> {}
#[stable(feature = "fused", since = "1.26.0")]
impl<I: FusedIterator> FusedIterator for Peekable<I> {}
impl<I: Iterator> Peekable<I> {
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn peek(&mut self) -> Option<&I::Item> {
        let iter = &mut self.iter;
        self.peeked.get_or_insert_with(|| iter.next()).as_ref()
    }
}
#[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(super) 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> {
        let flag = &mut self.flag;
        let pred = &mut self.predicate;
        self.iter.find(move |x| {
            if *flag || !pred(x) {
                *flag = true;
                true
            } else {
                false
            }
        })
    }
    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let (_, upper) = self.iter.size_hint();
        (0, upper) 
    }
    #[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<Ok=Acc>
    {
        if !self.flag {
            match self.next() {
                Some(v) => init = fold(init, v)?,
                None => return Try::from_ok(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 {}
#[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(super) 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 {
            self.iter.next().and_then(|x| {
                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) 
        }
    }
    #[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<Ok=Acc>
    {
        if self.flag {
            Try::from_ok(init)
        } else {
            let flag = &mut self.flag;
            let p = &mut self.predicate;
            self.iter.try_fold(init, move |acc, x|{
                if p(&x) {
                    LoopState::from_try(fold(acc, x))
                } else {
                    *flag = true;
                    LoopState::Break(Try::from_ok(acc))
                }
            }).into_try()
        }
    }
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I, P> FusedIterator for TakeWhile<I, P>
    where I: FusedIterator, P: FnMut(&I::Item) -> bool {}
#[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(super) 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 self.n == 0 {
            self.iter.next()
        } else {
            let old_n = self.n;
            self.n = 0;
            self.iter.nth(old_n)
        }
    }
    #[inline]
    fn nth(&mut self, n: usize) -> Option<I::Item> {
        
        if self.n == 0 {
            self.iter.nth(n)
        } else {
            let to_skip = self.n;
            self.n = 0;
            
            if self.iter.nth(to_skip-1).is_none() {
                return None;
            }
            self.iter.nth(n)
        }
    }
    #[inline]
    fn count(self) -> usize {
        self.iter.count().saturating_sub(self.n)
    }
    #[inline]
    fn last(mut self) -> Option<I::Item> {
        if self.n == 0 {
            self.iter.last()
        } else {
            let next = self.next();
            if next.is_some() {
                
                self.last().or(next)
            } else {
                None
            }
        }
    }
    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let (lower, upper) = self.iter.size_hint();
        let lower = lower.saturating_sub(self.n);
        let upper = upper.map(|x| x.saturating_sub(self.n));
        (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<Ok=Acc>
    {
        let n = self.n;
        self.n = 0;
        if n > 0 {
            
            if self.iter.nth(n - 1).is_none() {
                return Try::from_ok(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)
    }
}
#[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
        }
    }
    fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
        Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
    {
        let mut n = self.len();
        if n == 0 {
            Try::from_ok(init)
        } else {
            self.iter.try_rfold(init, move |acc, x| {
                n -= 1;
                let r = fold(acc, x);
                if n == 0 { LoopState::Break(r) }
                else { LoopState::from_try(r) }
            }).into_try()
        }
    }
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I> FusedIterator for Skip<I> where I: FusedIterator {}
#[derive(Clone, Debug)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Take<I> {
    pub(super) iter: I,
    pub(super) n: usize
}
impl<I> Take<I> {
    pub(super) fn new(iter: I, n: usize) -> Take<I> {
        Take { iter, n }
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> Iterator for Take<I> where I: Iterator{
    type Item = <I as Iterator>::Item;
    #[inline]
    fn next(&mut self) -> Option<<I as Iterator>::Item> {
        if self.n != 0 {
            self.n -= 1;
            self.iter.next()
        } else {
            None
        }
    }
    #[inline]
    fn nth(&mut self, n: usize) -> Option<I::Item> {
        if self.n > n {
            self.n -= n + 1;
            self.iter.nth(n)
        } else {
            if self.n > 0 {
                self.iter.nth(self.n - 1);
                self.n = 0;
            }
            None
        }
    }
    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        if self.n == 0 {
            return (0, Some(0));
        }
        let (lower, upper) = self.iter.size_hint();
        let lower = cmp::min(lower, self.n);
        let upper = match upper {
            Some(x) if x < self.n => Some(x),
            _ => Some(self.n)
        };
        (lower, upper)
    }
    #[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<Ok=Acc>
    {
        if self.n == 0 {
            Try::from_ok(init)
        } else {
            let n = &mut self.n;
            self.iter.try_fold(init, move |acc, x| {
                *n -= 1;
                let r = fold(acc, x);
                if *n == 0 { LoopState::Break(r) }
                else { LoopState::from_try(r) }
            }).into_try()
        }
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> ExactSizeIterator for Take<I> where I: ExactSizeIterator {}
#[stable(feature = "fused", since = "1.26.0")]
impl<I> FusedIterator for Take<I> where I: FusedIterator {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<I: TrustedLen> TrustedLen for Take<I> {}
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct Scan<I, St, F> {
    iter: I,
    f: F,
    state: St,
}
impl<I, St, F> Scan<I, St, F> {
    pub(super) fn new(iter: I, state: St, f: F) -> Scan<I, St, F> {
        Scan { iter, state, f }
    }
}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<I: fmt::Debug, St: fmt::Debug, F> fmt::Debug for Scan<I, St, F> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Scan")
            .field("iter", &self.iter)
            .field("state", &self.state)
            .finish()
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B, I, St, F> Iterator for Scan<I, St, F> where
    I: Iterator,
    F: FnMut(&mut St, I::Item) -> Option<B>,
{
    type Item = B;
    #[inline]
    fn next(&mut self) -> Option<B> {
        self.iter.next().and_then(|a| (self.f)(&mut self.state, a))
    }
    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let (_, upper) = self.iter.size_hint();
        (0, upper) 
    }
    #[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<Ok=Acc>
    {
        let state = &mut self.state;
        let f = &mut self.f;
        self.iter.try_fold(init, move |acc, x| {
            match f(state, x) {
                None => LoopState::Break(Try::from_ok(acc)),
                Some(x) => LoopState::from_try(fold(acc, x)),
            }
        }).into_try()
    }
}
#[derive(Clone, Debug)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Fuse<I> {
    iter: I,
    done: bool
}
impl<I> Fuse<I> {
    pub(super) fn new(iter: I) -> Fuse<I> {
        Fuse { iter, done: false }
    }
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I> FusedIterator for Fuse<I> where I: Iterator {}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> Iterator for Fuse<I> where I: Iterator {
    type Item = <I as Iterator>::Item;
    #[inline]
    default fn next(&mut self) -> Option<<I as Iterator>::Item> {
        if self.done {
            None
        } else {
            let next = self.iter.next();
            self.done = next.is_none();
            next
        }
    }
    #[inline]
    default fn nth(&mut self, n: usize) -> Option<I::Item> {
        if self.done {
            None
        } else {
            let nth = self.iter.nth(n);
            self.done = nth.is_none();
            nth
        }
    }
    #[inline]
    default fn last(self) -> Option<I::Item> {
        if self.done {
            None
        } else {
            self.iter.last()
        }
    }
    #[inline]
    default fn count(self) -> usize {
        if self.done {
            0
        } else {
            self.iter.count()
        }
    }
    #[inline]
    default fn size_hint(&self) -> (usize, Option<usize>) {
        if self.done {
            (0, Some(0))
        } else {
            self.iter.size_hint()
        }
    }
    #[inline]
    default fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
        Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
    {
        if self.done {
            Try::from_ok(init)
        } else {
            let acc = self.iter.try_fold(init, fold)?;
            self.done = true;
            Try::from_ok(acc)
        }
    }
    #[inline]
    default fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        if self.done {
            init
        } else {
            self.iter.fold(init, fold)
        }
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> DoubleEndedIterator for Fuse<I> where I: DoubleEndedIterator {
    #[inline]
    default fn next_back(&mut self) -> Option<<I as Iterator>::Item> {
        if self.done {
            None
        } else {
            let next = self.iter.next_back();
            self.done = next.is_none();
            next
        }
    }
    #[inline]
    default fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
        Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
    {
        if self.done {
            Try::from_ok(init)
        } else {
            let acc = self.iter.try_rfold(init, fold)?;
            self.done = true;
            Try::from_ok(acc)
        }
    }
    #[inline]
    default fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        if self.done {
            init
        } else {
            self.iter.rfold(init, fold)
        }
    }
}
unsafe impl<I> TrustedRandomAccess for Fuse<I>
    where I: TrustedRandomAccess,
{
    unsafe fn get_unchecked(&mut self, i: usize) -> I::Item {
        self.iter.get_unchecked(i)
    }
    fn may_have_side_effect() -> bool {
        I::may_have_side_effect()
    }
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I> Iterator for Fuse<I> where I: FusedIterator {
    #[inline]
    fn next(&mut self) -> Option<<I as Iterator>::Item> {
        self.iter.next()
    }
    #[inline]
    fn nth(&mut self, n: usize) -> Option<I::Item> {
        self.iter.nth(n)
    }
    #[inline]
    fn last(self) -> Option<I::Item> {
        self.iter.last()
    }
    #[inline]
    fn count(self) -> usize {
        self.iter.count()
    }
    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
    #[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<Ok=Acc>
    {
        self.iter.try_fold(init, fold)
    }
    #[inline]
    fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        self.iter.fold(init, fold)
    }
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I> DoubleEndedIterator for Fuse<I>
    where I: DoubleEndedIterator + FusedIterator
{
    #[inline]
    fn next_back(&mut self) -> Option<<I as Iterator>::Item> {
        self.iter.next_back()
    }
    #[inline]
    fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
        Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
    {
        self.iter.try_rfold(init, fold)
    }
    #[inline]
    fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        self.iter.rfold(init, fold)
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I> ExactSizeIterator for Fuse<I> where I: ExactSizeIterator {
    fn len(&self) -> usize {
        self.iter.len()
    }
    fn is_empty(&self) -> bool {
        self.iter.is_empty()
    }
}
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Clone)]
pub struct Inspect<I, F> {
    iter: I,
    f: F,
}
impl<I, F> Inspect<I, F> {
    pub(super) fn new(iter: I, f: F) -> Inspect<I, F> {
        Inspect { iter, f }
    }
}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<I: fmt::Debug, F> fmt::Debug for Inspect<I, F> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Inspect")
            .field("iter", &self.iter)
            .finish()
    }
}
impl<I: Iterator, F> Inspect<I, F> where F: FnMut(&I::Item) {
    #[inline]
    fn do_inspect(&mut self, elt: Option<I::Item>) -> Option<I::Item> {
        if let Some(ref a) = elt {
            (self.f)(a);
        }
        elt
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator, F> Iterator for Inspect<I, F> where F: FnMut(&I::Item) {
    type Item = I::Item;
    #[inline]
    fn next(&mut self) -> Option<I::Item> {
        let next = self.iter.next();
        self.do_inspect(next)
    }
    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
    #[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<Ok=Acc>
    {
        let f = &mut self.f;
        self.iter.try_fold(init, move |acc, item| { f(&item); fold(acc, item) })
    }
    #[inline]
    fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        let mut f = self.f;
        self.iter.fold(init, move |acc, item| { f(&item); fold(acc, item) })
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: DoubleEndedIterator, F> DoubleEndedIterator for Inspect<I, F>
    where F: FnMut(&I::Item),
{
    #[inline]
    fn next_back(&mut self) -> Option<I::Item> {
        let next = self.iter.next_back();
        self.do_inspect(next)
    }
    #[inline]
    fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
        Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
    {
        let f = &mut self.f;
        self.iter.try_rfold(init, move |acc, item| { f(&item); fold(acc, item) })
    }
    #[inline]
    fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        let mut f = self.f;
        self.iter.rfold(init, move |acc, item| { f(&item); fold(acc, item) })
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<I: ExactSizeIterator, F> ExactSizeIterator for Inspect<I, F>
    where F: FnMut(&I::Item)
{
    fn len(&self) -> usize {
        self.iter.len()
    }
    fn is_empty(&self) -> bool {
        self.iter.is_empty()
    }
}
#[stable(feature = "fused", since = "1.26.0")]
impl<I: FusedIterator, F> FusedIterator for Inspect<I, F>
    where F: FnMut(&I::Item) {}