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    use crate::alloc::{Allocator, Global};
    use crate::raw_vec::RawVec;
    use core::fmt;
    use core::intrinsics::arith_offset;
    use core::iter::{FusedIterator, InPlaceIterable, SourceIter, TrustedLen, TrustedRandomAccess};
    use core::marker::PhantomData;
    use core::mem::{self};
    use core::ptr::{self, NonNull};
    use core::slice::{self};

    /// An iterator that moves out of a vector.
    ///
    /// This `struct` is created by the `into_iter` method on [`Vec`](super::Vec)
    /// (provided by the [`IntoIterator`] trait).
    ///
    /// # Example
    ///
    /// ```
    /// let v = vec![0, 1, 2];
    /// let iter: std::vec::IntoIter<_> = v.into_iter();
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct IntoIter<
        T,
        #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
    > {
        pub(super) buf: NonNull<T>,
        pub(super) phantom: PhantomData<T>,
        pub(super) cap: usize,
        pub(super) alloc: A,
        pub(super) ptr: *const T,
        pub(super) end: *const T,
    }

    #[stable(feature = "vec_intoiter_debug", since = "1.13.0")]
    impl<T: fmt::Debug, A: Allocator> fmt::Debug for IntoIter<T, A> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.debug_tuple("IntoIter").field(&self.as_slice()).finish()
        }
    }

    impl<T, A: Allocator> IntoIter<T, A> {
        /// Returns the remaining items of this iterator as a slice.
        ///
        /// # Examples
        ///
        /// ```
        /// let vec = vec!['a', 'b', 'c'];
        /// let mut into_iter = vec.into_iter();
        /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
        /// let _ = into_iter.next().unwrap();
        /// assert_eq!(into_iter.as_slice(), &['b', 'c']);
        /// ```
        #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
        pub fn as_slice(&self) -> &[T] {
            unsafe { slice::from_raw_parts(self.ptr, self.len()) }
        }

        /// Returns the remaining items of this iterator as a mutable slice.
        ///
        /// # Examples
        ///
        /// ```
        /// let vec = vec!['a', 'b', 'c'];
        /// let mut into_iter = vec.into_iter();
        /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
        /// into_iter.as_mut_slice()[2] = 'z';
        /// assert_eq!(into_iter.next().unwrap(), 'a');
        /// assert_eq!(into_iter.next().unwrap(), 'b');
        /// assert_eq!(into_iter.next().unwrap(), 'z');
        /// ```
        #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
        pub fn as_mut_slice(&mut self) -> &mut [T] {
            unsafe { &mut *self.as_raw_mut_slice() }
        }

        /// Returns a reference to the underlying allocator.
        #[unstable(feature = "allocator_api", issue = "32838")]
        #[inline]
        pub fn allocator(&self) -> &A {
            &self.alloc
        }

        fn as_raw_mut_slice(&mut self) -> *mut [T] {
            ptr::slice_from_raw_parts_mut(self.ptr as *mut T, self.len())
        }

        pub(super) fn drop_remaining(&mut self) {
            unsafe {
                ptr::drop_in_place(self.as_mut_slice());
            }
            self.ptr = self.end;
        }

        /// Relinquishes the backing allocation, equivalent to
        /// `ptr::write(&mut self, Vec::new().into_iter())`
        pub(super) fn forget_allocation(&mut self) {
            self.cap = 0;
            self.buf = unsafe { NonNull::new_unchecked(RawVec::NEW.ptr()) };
            self.ptr = self.buf.as_ptr();
            self.end = self.buf.as_ptr();
        }
    }

    #[stable(feature = "vec_intoiter_as_ref", since = "1.46.0")]
    impl<T, A: Allocator> AsRef<[T]> for IntoIter<T, A> {
        fn as_ref(&self) -> &[T] {
            self.as_slice()
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    unsafe impl<T: Send, A: Allocator + Send> Send for IntoIter<T, A> {}
    #[stable(feature = "rust1", since = "1.0.0")]
    unsafe impl<T: Sync, A: Allocator> Sync for IntoIter<T, A> {}

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T, A: Allocator> Iterator for IntoIter<T, A> {
        type Item = T;

        #[inline]
        fn next(&mut self) -> Option<T> {
            if self.ptr as *const _ == self.end {
                None
            } else if mem::size_of::<T>() == 0 {
                // purposefully don't use 'ptr.offset' because for
                // vectors with 0-size elements this would return the
                // same pointer.
                self.ptr = unsafe { arith_offset(self.ptr as *const i8, 1) as *mut T };

                // Make up a value of this ZST.
                Some(unsafe { mem::zeroed() })
            } else {
                let old = self.ptr;
                self.ptr = unsafe { self.ptr.offset(1) };

                Some(unsafe { ptr::read(old) })
            }
        }

        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            let exact = if mem::size_of::<T>() == 0 {
                (self.end as usize).wrapping_sub(self.ptr as usize)
            } else {
                unsafe { self.end.offset_from(self.ptr) as usize }
            };
            (exact, Some(exact))
        }

        #[inline]
        fn count(self) -> usize {
            self.len()
        }

        unsafe fn __iterator_get_unchecked(&mut self, i: usize) -> Self::Item
        where
            Self: TrustedRandomAccess,
        {
            // SAFETY: the caller must guarantee that `i` is in bounds of the
            // `Vec<T>`, so `i` cannot overflow an `isize`, and the `self.ptr.add(i)`
            // is guaranteed to pointer to an element of the `Vec<T>` and
            // thus guaranteed to be valid to dereference.
            //
            // Also note the implementation of `Self: TrustedRandomAccess` requires
            // that `T: Copy` so reading elements from the buffer doesn't invalidate
            // them for `Drop`.
            unsafe {
                if mem::size_of::<T>() == 0 { mem::zeroed() } else { ptr::read(self.ptr.add(i)) }
            }
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
        #[inline]
        fn next_back(&mut self) -> Option<T> {
            if self.end == self.ptr {
                None
            } else if mem::size_of::<T>() == 0 {
                // See above for why 'ptr.offset' isn't used
                self.end = unsafe { arith_offset(self.end as *const i8, -1) as *mut T };

                // Make up a value of this ZST.
                Some(unsafe { mem::zeroed() })
            } else {
                self.end = unsafe { self.end.offset(-1) };

                Some(unsafe { ptr::read(self.end) })
            }
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T, A: Allocator> ExactSizeIterator for IntoIter<T, A> {
        fn is_empty(&self) -> bool {
            self.ptr == self.end
        }
    }

    #[stable(feature = "fused", since = "1.26.0")]
    impl<T, A: Allocator> FusedIterator for IntoIter<T, A> {}

    #[unstable(feature = "trusted_len", issue = "37572")]
    unsafe impl<T, A: Allocator> TrustedLen for IntoIter<T, A> {}

    #[doc(hidden)]
    #[unstable(issue = "none", feature = "std_internals")]
    // T: Copy as approximation for !Drop since get_unchecked does not advance self.ptr
    // and thus we can't implement drop-handling
    unsafe impl<T, A: Allocator> TrustedRandomAccess for IntoIter<T, A>
    where
        T: Copy,
    {
        const MAY_HAVE_SIDE_EFFECT: bool = false;
    }

    #[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
    impl<T: Clone, A: Allocator + Clone> Clone for IntoIter<T, A> {
        #[cfg(not(test))]
        fn clone(&self) -> Self {
            self.as_slice().to_vec_in(self.alloc.clone()).into_iter()
        }
        #[cfg(test)]
        fn clone(&self) -> Self {
            crate::slice::to_vec(self.as_slice(), self.alloc.clone()).into_iter()
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    unsafe impl<#[may_dangle] T, A: Allocator> Drop for IntoIter<T, A> {
        fn drop(&mut self) {
            struct DropGuard<'a, T, A: Allocator>(&'a mut IntoIter<T, A>);

            impl<T, A: Allocator> Drop for DropGuard<'_, T, A> {
                fn drop(&mut self) {
                    unsafe {
                        // `IntoIter::alloc` is not used anymore after this
                        let alloc = ptr::read(&self.0.alloc);
                        // RawVec handles deallocation
                        let _ = RawVec::from_raw_parts_in(self.0.buf.as_ptr(), self.0.cap, alloc);
                    }
                }
            }

            let guard = DropGuard(self);
            // destroy the remaining elements
            unsafe {
                ptr::drop_in_place(guard.0.as_raw_mut_slice());
            }
            // now `guard` will be dropped and do the rest
        }
    }

    #[unstable(issue = "none", feature = "inplace_iteration")]
    unsafe impl<T, A: Allocator> InPlaceIterable for IntoIter<T, A> {}

    #[unstable(issue = "none", feature = "inplace_iteration")]
    unsafe impl<T, A: Allocator> SourceIter for IntoIter<T, A> {
        type Source = Self;

        #[inline]
        unsafe fn as_inner(&mut self) -> &mut Self::Source {
            self
        }
    }

    // internal helper trait for in-place iteration specialization.
    #[rustc_specialization_trait]
    pub(crate) trait AsIntoIter {
        type Item;
        fn as_into_iter(&mut self) -> &mut IntoIter<Self::Item>;
    }

    impl<T> AsIntoIter for IntoIter<T> {
        type Item = T;

        fn as_into_iter(&mut self) -> &mut IntoIter<Self::Item> {
            self
        }
    }