mod.rs

// Copyright 2014-2016 bluss and ndarray developers.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

#[macro_use]
mod macros;
mod chunks;
mod into_iter;
pub mod iter;
mod lanes;
mod windows;

#[cfg(not(feature = "std"))]
use alloc::vec::Vec;
use std::iter::FromIterator;
use std::marker::PhantomData;
use std::ptr;
use std::ptr::NonNull;

#[allow(unused_imports)] // Needed for Rust 1.64
use rawpointer::PointerExt;

use crate::Ix1;

use super::{ArrayBase, ArrayView, ArrayViewMut, Axis, Data, NdProducer, RemoveAxis};
use super::{Dimension, Ix, Ixs};

pub use self::chunks::{ExactChunks, ExactChunksIter, ExactChunksIterMut, ExactChunksMut};
pub use self::into_iter::IntoIter;
pub use self::lanes::{Lanes, LanesMut};
pub use self::windows::{AxisWindows, Windows};

use std::slice::{self, Iter as SliceIter, IterMut as SliceIterMut};

/// Base for iterators over all axes.
///
/// Iterator element type is `NonNull<A>`.
#[derive(Debug)]
pub struct Baseiter<A, D>
{
    ptr: NonNull<A>,
    dim: D,
    strides: D,
    index: Option<D>,
}

impl<A, D: Dimension> Baseiter<A, D>
{
    /// Creating a Baseiter is unsafe because shape and stride parameters need
    /// to be correct to avoid performing an unsafe pointer offset while
    /// iterating.
    #[inline]
    pub unsafe fn new(ptr: NonNull<A>, len: D, stride: D) -> Baseiter<A, D>
    {
        Baseiter {
            ptr,
            index: len.first_index(),
            dim: len,
            strides: stride,
        }
    }
}

impl<A, D: Dimension> Iterator for Baseiter<A, D>
{
    type Item = NonNull<A>;

    #[inline]
    fn next(&mut self) -> Option<Self::Item>
    {
        let index = match self.index {
            None => return None,
            Some(ref ix) => ix.clone(),
        };
        let offset = D::stride_offset(&index, &self.strides);
        self.index = self.dim.next_for(index);
        unsafe { Some(self.ptr.offset(offset)) }
    }

    fn size_hint(&self) -> (usize, Option<usize>)
    {
        let len = self.len();
        (len, Some(len))
    }

    fn fold<Acc, G>(mut self, init: Acc, mut g: G) -> Acc
    where G: FnMut(Acc, Self::Item) -> Acc
    {
        let ndim = self.dim.ndim();
        debug_assert_ne!(ndim, 0);
        let mut accum = init;
        while let Some(mut index) = self.index {
            let stride = self.strides.last_elem() as isize;
            let elem_index = index.last_elem();
            let len = self.dim.last_elem();
            let offset = D::stride_offset(&index, &self.strides);
            unsafe {
                let row_ptr = self.ptr.offset(offset);
                let mut i = 0;
                let i_end = len - elem_index;
                while i < i_end {
                    accum = g(accum, row_ptr.offset(i as isize * stride));
                    i += 1;
                }
            }
            index.set_last_elem(len - 1);
            self.index = self.dim.next_for(index);
        }
        accum
    }
}

impl<A, D: Dimension> ExactSizeIterator for Baseiter<A, D>
{
    fn len(&self) -> usize
    {
        match self.index {
            None => 0,
            Some(ref ix) => {
                let gone = self
                    .dim
                    .default_strides()
                    .slice()
                    .iter()
                    .zip(ix.slice().iter())
                    .fold(0, |s, (&a, &b)| s + a * b);
                self.dim.size() - gone
            }
        }
    }
}

impl<A> DoubleEndedIterator for Baseiter<A, Ix1>
{
    #[inline]
    fn next_back(&mut self) -> Option<Self::Item>
    {
        let index = self.index?;
        self.dim[0] -= 1;
        let offset = Ix1::stride_offset(&self.dim, &self.strides);
        if index == self.dim {
            self.index = None;
        }

        unsafe { Some(self.ptr.offset(offset)) }
    }

    fn nth_back(&mut self, n: usize) -> Option<Self::Item>
    {
        let index = self.index?;
        let len = self.dim[0] - index[0];
        if n < len {
            self.dim[0] -= n + 1;
            let offset = Ix1::stride_offset(&self.dim, &self.strides);
            if index == self.dim {
                self.index = None;
            }
            unsafe { Some(self.ptr.offset(offset)) }
        } else {
            self.index = None;
            None
        }
    }

    fn rfold<Acc, G>(mut self, init: Acc, mut g: G) -> Acc
    where G: FnMut(Acc, Self::Item) -> Acc
    {
        let mut accum = init;
        if let Some(index) = self.index {
            let elem_index = index[0];
            unsafe {
                // self.dim[0] is the current length
                while self.dim[0] > elem_index {
                    self.dim[0] -= 1;
                    accum = g(
                        accum,
                        self.ptr
                            .offset(Ix1::stride_offset(&self.dim, &self.strides)),
                    );
                }
            }
        }
        accum
    }
}

clone_bounds!(
    [A, D: Clone]
    Baseiter[A, D] {
        @copy {
            ptr,
        }
        dim,
        strides,
        index,
    }
);

clone_bounds!(
    ['a, A, D: Clone]
    ElementsBase['a, A, D] {
        @copy {
            life,
        }
        inner,
    }
);

impl<'a, A, D: Dimension> ElementsBase<'a, A, D>
{
    pub fn new(v: ArrayView<'a, A, D>) -> Self
    {
        ElementsBase {
            inner: v.into_base_iter(),
            life: PhantomData,
        }
    }
}

impl<'a, A, D: Dimension> Iterator for ElementsBase<'a, A, D>
{
    type Item = &'a A;
    #[inline]
    fn next(&mut self) -> Option<&'a A>
    {
        self.inner.next().map(|p| unsafe { p.as_ref() })
    }

    fn size_hint(&self) -> (usize, Option<usize>)
    {
        self.inner.size_hint()
    }

    fn fold<Acc, G>(self, init: Acc, mut g: G) -> Acc
    where G: FnMut(Acc, Self::Item) -> Acc
    {
        unsafe { self.inner.fold(init, move |acc, ptr| g(acc, ptr.as_ref())) }
    }
}

impl<'a, A> DoubleEndedIterator for ElementsBase<'a, A, Ix1>
{
    #[inline]
    fn next_back(&mut self) -> Option<&'a A>
    {
        self.inner.next_back().map(|p| unsafe { p.as_ref() })
    }

    fn rfold<Acc, G>(self, init: Acc, mut g: G) -> Acc
    where G: FnMut(Acc, Self::Item) -> Acc
    {
        unsafe { self.inner.rfold(init, move |acc, ptr| g(acc, ptr.as_ref())) }
    }
}

impl<A, D> ExactSizeIterator for ElementsBase<'_, A, D>
where D: Dimension
{
    fn len(&self) -> usize
    {
        self.inner.len()
    }
}

macro_rules! either {
    ($value:expr, $inner:pat => $result:expr) => {
        match $value {
            ElementsRepr::Slice($inner) => $result,
            ElementsRepr::Counted($inner) => $result,
        }
    };
}

macro_rules! either_mut {
    ($value:expr, $inner:ident => $result:expr) => {
        match $value {
            ElementsRepr::Slice(ref mut $inner) => $result,
            ElementsRepr::Counted(ref mut $inner) => $result,
        }
    };
}

clone_bounds!(
    ['a, A, D: Clone]
    Iter['a, A, D] {
        @copy {
        }
        inner,
    }
);

impl<'a, A, D> Iter<'a, A, D>
where D: Dimension
{
    pub(crate) fn new(self_: ArrayView<'a, A, D>) -> Self
    {
        Iter {
            inner: if let Some(slc) = self_.to_slice() {
                ElementsRepr::Slice(slc.iter())
            } else {
                ElementsRepr::Counted(self_.into_elements_base())
            },
        }
    }
}

impl<'a, A, D> IterMut<'a, A, D>
where D: Dimension
{
    pub(crate) fn new(self_: ArrayViewMut<'a, A, D>) -> Self
    {
        IterMut {
            inner: match self_.try_into_slice() {
                Ok(x) => ElementsRepr::Slice(x.iter_mut()),
                Err(self_) => ElementsRepr::Counted(self_.into_elements_base()),
            },
        }
    }
}

#[derive(Clone, Debug)]
pub enum ElementsRepr<S, C>
{
    Slice(S),
    Counted(C),
}

/// An iterator over the elements of an array.
///
/// Iterator element type is `&'a A`.
///
/// See [`.iter()`](crate::ArrayRef::iter) for more information.
#[derive(Debug)]
pub struct Iter<'a, A, D>
{
    inner: ElementsRepr<SliceIter<'a, A>, ElementsBase<'a, A, D>>,
}

/// Counted read only iterator
#[derive(Debug)]
pub struct ElementsBase<'a, A, D>
{
    inner: Baseiter<A, D>,
    life: PhantomData<&'a A>,
}

/// An iterator over the elements of an array (mutable).
///
/// Iterator element type is `&'a mut A`.
///
/// See [`.iter_mut()`](crate::ArrayRef::iter_mut) for more information.
#[derive(Debug)]
pub struct IterMut<'a, A, D>
{
    inner: ElementsRepr<SliceIterMut<'a, A>, ElementsBaseMut<'a, A, D>>,
}

/// An iterator over the elements of an array.
///
/// Iterator element type is `&'a mut A`.
#[derive(Debug)]
pub struct ElementsBaseMut<'a, A, D>
{
    inner: Baseiter<A, D>,
    life: PhantomData<&'a mut A>,
}

impl<'a, A, D: Dimension> ElementsBaseMut<'a, A, D>
{
    pub fn new(v: ArrayViewMut<'a, A, D>) -> Self
    {
        ElementsBaseMut {
            inner: v.into_base_iter(),
            life: PhantomData,
        }
    }
}

/// An iterator over the indexes and elements of an array.
///
/// See [`.indexed_iter()`](crate::ArrayRef::indexed_iter) for more information.
#[derive(Clone)]
pub struct IndexedIter<'a, A, D>(ElementsBase<'a, A, D>);
/// An iterator over the indexes and elements of an array (mutable).
///
/// See [`.indexed_iter_mut()`](crate::ArrayRef::indexed_iter_mut) for more information.
pub struct IndexedIterMut<'a, A, D>(ElementsBaseMut<'a, A, D>);

impl<'a, A, D> IndexedIter<'a, A, D>
where D: Dimension
{
    pub(crate) fn new(x: ElementsBase<'a, A, D>) -> Self
    {
        IndexedIter(x)
    }
}

impl<'a, A, D> IndexedIterMut<'a, A, D>
where D: Dimension
{
    pub(crate) fn new(x: ElementsBaseMut<'a, A, D>) -> Self
    {
        IndexedIterMut(x)
    }
}

impl<'a, A, D: Dimension> Iterator for Iter<'a, A, D>
{
    type Item = &'a A;
    #[inline]
    fn next(&mut self) -> Option<&'a A>
    {
        either_mut!(self.inner, iter => iter.next())
    }

    fn size_hint(&self) -> (usize, Option<usize>)
    {
        either!(self.inner, ref iter => iter.size_hint())
    }

    fn fold<Acc, G>(self, init: Acc, g: G) -> Acc
    where G: FnMut(Acc, Self::Item) -> Acc
    {
        either!(self.inner, iter => iter.fold(init, g))
    }

    fn nth(&mut self, n: usize) -> Option<Self::Item>
    {
        either_mut!(self.inner, iter => iter.nth(n))
    }

    fn collect<B>(self) -> B
    where B: FromIterator<Self::Item>
    {
        either!(self.inner, iter => iter.collect())
    }

    fn all<F>(&mut self, f: F) -> bool
    where F: FnMut(Self::Item) -> bool
    {
        either_mut!(self.inner, iter => iter.all(f))
    }

    fn any<F>(&mut self, f: F) -> bool
    where F: FnMut(Self::Item) -> bool
    {
        either_mut!(self.inner, iter => iter.any(f))
    }

    fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
    where P: FnMut(&Self::Item) -> bool
    {
        either_mut!(self.inner, iter => iter.find(predicate))
    }

    fn find_map<B, F>(&mut self, f: F) -> Option<B>
    where F: FnMut(Self::Item) -> Option<B>
    {
        either_mut!(self.inner, iter => iter.find_map(f))
    }

    fn count(self) -> usize
    {
        either!(self.inner, iter => iter.count())
    }

    fn last(self) -> Option<Self::Item>
    {
        either!(self.inner, iter => iter.last())
    }

    fn position<P>(&mut self, predicate: P) -> Option<usize>
    where P: FnMut(Self::Item) -> bool
    {
        either_mut!(self.inner, iter => iter.position(predicate))
    }
}

impl<'a, A> DoubleEndedIterator for Iter<'a, A, Ix1>
{
    #[inline]
    fn next_back(&mut self) -> Option<&'a A>
    {
        either_mut!(self.inner, iter => iter.next_back())
    }

    fn nth_back(&mut self, n: usize) -> Option<&'a A>
    {
        either_mut!(self.inner, iter => iter.nth_back(n))
    }

    fn rfold<Acc, G>(self, init: Acc, g: G) -> Acc
    where G: FnMut(Acc, Self::Item) -> Acc
    {
        either!(self.inner, iter => iter.rfold(init, g))
    }
}

impl<A, D> ExactSizeIterator for Iter<'_, A, D>
where D: Dimension
{
    fn len(&self) -> usize
    {
        either!(self.inner, ref iter => iter.len())
    }
}

impl<'a, A, D: Dimension> Iterator for IndexedIter<'a, A, D>
{
    type Item = (D::Pattern, &'a A);
    #[inline]
    fn next(&mut self) -> Option<Self::Item>
    {
        let index = match self.0.inner.index {
            None => return None,
            Some(ref ix) => ix.clone(),
        };
        match self.0.next() {
            None => None,
            Some(elem) => Some((index.into_pattern(), elem)),
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>)
    {
        self.0.size_hint()
    }
}

impl<A, D> ExactSizeIterator for IndexedIter<'_, A, D>
where D: Dimension
{
    fn len(&self) -> usize
    {
        self.0.inner.len()
    }
}

impl<'a, A, D: Dimension> Iterator for IterMut<'a, A, D>
{
    type Item = &'a mut A;
    #[inline]
    fn next(&mut self) -> Option<&'a mut A>
    {
        either_mut!(self.inner, iter => iter.next())
    }

    fn size_hint(&self) -> (usize, Option<usize>)
    {
        either!(self.inner, ref iter => iter.size_hint())
    }

    fn fold<Acc, G>(self, init: Acc, g: G) -> Acc
    where G: FnMut(Acc, Self::Item) -> Acc
    {
        either!(self.inner, iter => iter.fold(init, g))
    }

    fn nth(&mut self, n: usize) -> Option<Self::Item>
    {
        either_mut!(self.inner, iter => iter.nth(n))
    }

    fn collect<B>(self) -> B
    where B: FromIterator<Self::Item>
    {
        either!(self.inner, iter => iter.collect())
    }

    fn all<F>(&mut self, f: F) -> bool
    where F: FnMut(Self::Item) -> bool
    {
        either_mut!(self.inner, iter => iter.all(f))
    }

    fn any<F>(&mut self, f: F) -> bool
    where F: FnMut(Self::Item) -> bool
    {
        either_mut!(self.inner, iter => iter.any(f))
    }

    fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
    where P: FnMut(&Self::Item) -> bool
    {
        either_mut!(self.inner, iter => iter.find(predicate))
    }

    fn find_map<B, F>(&mut self, f: F) -> Option<B>
    where F: FnMut(Self::Item) -> Option<B>
    {
        either_mut!(self.inner, iter => iter.find_map(f))
    }

    fn count(self) -> usize
    {
        either!(self.inner, iter => iter.count())
    }

    fn last(self) -> Option<Self::Item>
    {
        either!(self.inner, iter => iter.last())
    }

    fn position<P>(&mut self, predicate: P) -> Option<usize>
    where P: FnMut(Self::Item) -> bool
    {
        either_mut!(self.inner, iter => iter.position(predicate))
    }
}

impl<'a, A> DoubleEndedIterator for IterMut<'a, A, Ix1>
{
    #[inline]
    fn next_back(&mut self) -> Option<&'a mut A>
    {
        either_mut!(self.inner, iter => iter.next_back())
    }

    fn nth_back(&mut self, n: usize) -> Option<&'a mut A>
    {
        either_mut!(self.inner, iter => iter.nth_back(n))
    }

    fn rfold<Acc, G>(self, init: Acc, g: G) -> Acc
    where G: FnMut(Acc, Self::Item) -> Acc
    {
        either!(self.inner, iter => iter.rfold(init, g))
    }
}

impl<A, D> ExactSizeIterator for IterMut<'_, A, D>
where D: Dimension
{
    fn len(&self) -> usize
    {
        either!(self.inner, ref iter => iter.len())
    }
}

impl<'a, A, D: Dimension> Iterator for ElementsBaseMut<'a, A, D>
{
    type Item = &'a mut A;
    #[inline]
    fn next(&mut self) -> Option<&'a mut A>
    {
        self.inner.next().map(|mut p| unsafe { p.as_mut() })
    }

    fn size_hint(&self) -> (usize, Option<usize>)
    {
        self.inner.size_hint()
    }

    fn fold<Acc, G>(self, init: Acc, mut g: G) -> Acc
    where G: FnMut(Acc, Self::Item) -> Acc
    {
        unsafe {
            self.inner
                .fold(init, move |acc, mut ptr| g(acc, ptr.as_mut()))
        }
    }
}

impl<'a, A> DoubleEndedIterator for ElementsBaseMut<'a, A, Ix1>
{
    #[inline]
    fn next_back(&mut self) -> Option<&'a mut A>
    {
        self.inner.next_back().map(|mut p| unsafe { p.as_mut() })
    }

    fn rfold<Acc, G>(self, init: Acc, mut g: G) -> Acc
    where G: FnMut(Acc, Self::Item) -> Acc
    {
        unsafe {
            self.inner
                .rfold(init, move |acc, mut ptr| g(acc, ptr.as_mut()))
        }
    }
}

impl<A, D> ExactSizeIterator for ElementsBaseMut<'_, A, D>
where D: Dimension
{
    fn len(&self) -> usize
    {
        self.inner.len()
    }
}

impl<'a, A, D: Dimension> Iterator for IndexedIterMut<'a, A, D>
{
    type Item = (D::Pattern, &'a mut A);
    #[inline]
    fn next(&mut self) -> Option<Self::Item>
    {
        let index = match self.0.inner.index {
            None => return None,
            Some(ref ix) => ix.clone(),
        };
        match self.0.next() {
            None => None,
            Some(elem) => Some((index.into_pattern(), elem)),
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>)
    {
        self.0.size_hint()
    }
}

impl<A, D> ExactSizeIterator for IndexedIterMut<'_, A, D>
where D: Dimension
{
    fn len(&self) -> usize
    {
        self.0.inner.len()
    }
}

/// An iterator that traverses over all axes but one, and yields a view for
/// each lane along that axis.
///
/// See [`.lanes()`](crate::ArrayRef::lanes) for more information.
pub struct LanesIter<'a, A, D>
{
    inner_len: Ix,
    inner_stride: Ixs,
    iter: Baseiter<A, D>,
    life: PhantomData<&'a A>,
}

clone_bounds!(
    ['a, A, D: Clone]
    LanesIter['a, A, D] {
        @copy {
            inner_len,
            inner_stride,
            life,
        }
        iter,
    }
);

impl<'a, A, D> Iterator for LanesIter<'a, A, D>
where D: Dimension
{
    type Item = ArrayView<'a, A, Ix1>;
    fn next(&mut self) -> Option<Self::Item>
    {
        self.iter
            .next()
            .map(|ptr| unsafe { ArrayView::new(ptr, Ix1(self.inner_len), Ix1(self.inner_stride as Ix)) })
    }

    fn size_hint(&self) -> (usize, Option<usize>)
    {
        self.iter.size_hint()
    }
}

impl<A, D> ExactSizeIterator for LanesIter<'_, A, D>
where D: Dimension
{
    fn len(&self) -> usize
    {
        self.iter.len()
    }
}

impl<A> DoubleEndedIterator for LanesIter<'_, A, Ix1>
{
    fn next_back(&mut self) -> Option<Self::Item>
    {
        self.iter
            .next_back()
            .map(|ptr| unsafe { ArrayView::new(ptr, Ix1(self.inner_len), Ix1(self.inner_stride as Ix)) })
    }
}

// NOTE: LanesIterMut is a mutable iterator and must not expose aliasing
// pointers. Due to this we use an empty slice for the raw data (it's unused
// anyway).
/// An iterator that traverses over all dimensions but the innermost,
/// and yields each inner row (mutable).
///
/// See [`.lanes_mut()`](crate::ArrayRef::lanes_mut)
/// for more information.
pub struct LanesIterMut<'a, A, D>
{
    inner_len: Ix,
    inner_stride: Ixs,
    iter: Baseiter<A, D>,
    life: PhantomData<&'a mut A>,
}

impl<'a, A, D> Iterator for LanesIterMut<'a, A, D>
where D: Dimension
{
    type Item = ArrayViewMut<'a, A, Ix1>;
    fn next(&mut self) -> Option<Self::Item>
    {
        self.iter
            .next()
            .map(|ptr| unsafe { ArrayViewMut::new(ptr, Ix1(self.inner_len), Ix1(self.inner_stride as Ix)) })
    }

    fn size_hint(&self) -> (usize, Option<usize>)
    {
        self.iter.size_hint()
    }
}

impl<A, D> ExactSizeIterator for LanesIterMut<'_, A, D>
where D: Dimension
{
    fn len(&self) -> usize
    {
        self.iter.len()
    }
}

impl<A> DoubleEndedIterator for LanesIterMut<'_, A, Ix1>
{
    fn next_back(&mut self) -> Option<Self::Item>
    {
        self.iter
            .next_back()
            .map(|ptr| unsafe { ArrayViewMut::new(ptr, Ix1(self.inner_len), Ix1(self.inner_stride as Ix)) })
    }
}

#[derive(Debug)]
pub struct AxisIterCore<A, D>
{
    /// Index along the axis of the value of `.next()`, relative to the start
    /// of the axis.
    index: Ix,
    /// (Exclusive) upper bound on `index`. Initially, this is equal to the
    /// length of the axis.
    end: Ix,
    /// Stride along the axis (offset between consecutive pointers).
    stride: Ixs,
    /// Shape of the iterator's items.
    inner_dim: D,
    /// Strides of the iterator's items.
    inner_strides: D,
    /// Pointer corresponding to `index == 0`.
    ptr: *mut A,
}

clone_bounds!(
    [A, D: Clone]
    AxisIterCore[A, D] {
        @copy {
            index,
            end,
            stride,
            ptr,
        }
        inner_dim,
        inner_strides,
    }
);

impl<A, D: Dimension> AxisIterCore<A, D>
{
    /// Constructs a new iterator over the specified axis.
    fn new<S, Di>(v: ArrayBase<S, Di>, axis: Axis) -> Self
    where
        Di: RemoveAxis<Smaller = D>,
        S: Data<Elem = A>,
    {
        AxisIterCore {
            index: 0,
            end: v.len_of(axis),
            stride: v.stride_of(axis),
            inner_dim: v.dim.remove_axis(axis),
            inner_strides: v.strides.remove_axis(axis),
            ptr: v.ptr.as_ptr(),
        }
    }

    #[inline]
    unsafe fn offset(&self, index: usize) -> *mut A
    {
        debug_assert!(
            index < self.end,
            "index={}, end={}, stride={}",
            index,
            self.end,
            self.stride
        );
        self.ptr.offset(index as isize * self.stride)
    }

    /// Splits the iterator at `index`, yielding two disjoint iterators.
    ///
    /// `index` is relative to the current state of the iterator (which is not
    /// necessarily the start of the axis).
    ///
    /// **Panics** if `index` is strictly greater than the iterator's remaining
    /// length.
    #[track_caller]
    fn split_at(self, index: usize) -> (Self, Self)
    {
        assert!(index <= self.len());
        let mid = self.index + index;
        let left = AxisIterCore {
            index: self.index,
            end: mid,
            stride: self.stride,
            inner_dim: self.inner_dim.clone(),
            inner_strides: self.inner_strides.clone(),
            ptr: self.ptr,
        };
        let right = AxisIterCore {
            index: mid,
            end: self.end,
            stride: self.stride,
            inner_dim: self.inner_dim,
            inner_strides: self.inner_strides,
            ptr: self.ptr,
        };
        (left, right)
    }

    /// Does the same thing as `.next()` but also returns the index of the item
    /// relative to the start of the axis.
    fn next_with_index(&mut self) -> Option<(usize, *mut A)>
    {
        let index = self.index;
        self.next().map(|ptr| (index, ptr))
    }

    /// Does the same thing as `.next_back()` but also returns the index of the
    /// item relative to the start of the axis.
    fn next_back_with_index(&mut self) -> Option<(usize, *mut A)>
    {
        self.next_back().map(|ptr| (self.end, ptr))
    }
}

impl<A, D> Iterator for AxisIterCore<A, D>
where D: Dimension
{
    type Item = *mut A;

    fn next(&mut self) -> Option<Self::Item>
    {
        if self.index >= self.end {
            None
        } else {
            let ptr = unsafe { self.offset(self.index) };
            self.index += 1;
            Some(ptr)
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>)
    {
        let len = self.len();
        (len, Some(len))
    }
}

impl<A, D> DoubleEndedIterator for AxisIterCore<A, D>
where D: Dimension
{
    fn next_back(&mut self) -> Option<Self::Item>
    {
        if self.index >= self.end {
            None
        } else {
            let ptr = unsafe { self.offset(self.end - 1) };
            self.end -= 1;
            Some(ptr)
        }
    }
}

impl<A, D> ExactSizeIterator for AxisIterCore<A, D>
where D: Dimension
{
    fn len(&self) -> usize
    {
        self.end - self.index
    }
}

/// An iterator that traverses over an axis and
/// and yields each subview.
///
/// The outermost dimension is `Axis(0)`, created with `.outer_iter()`,
/// but you can traverse arbitrary dimension with `.axis_iter()`.
///
/// For example, in a 3 × 5 × 5 array, with `axis` equal to `Axis(2)`,
/// the iterator element is a 3 × 5 subview (and there are 5 in total).
///
/// Iterator element type is `ArrayView<'a, A, D>`.
///
/// See [`.outer_iter()`](crate::ArrayRef::outer_iter)
/// or [`.axis_iter()`](crate::ArrayRef::axis_iter)
/// for more information.
#[derive(Debug)]
pub struct AxisIter<'a, A, D>
{
    iter: AxisIterCore<A, D>,
    life: PhantomData<&'a A>,
}

clone_bounds!(
    ['a, A, D: Clone]
    AxisIter['a, A, D] {
        @copy {
            life,
        }
        iter,
    }
);

impl<'a, A, D: Dimension> AxisIter<'a, A, D>
{
    /// Creates a new iterator over the specified axis.
    pub(crate) fn new<Di>(v: ArrayView<'a, A, Di>, axis: Axis) -> Self
    where Di: RemoveAxis<Smaller = D>
    {
        AxisIter {
            iter: AxisIterCore::new(v, axis),
            life: PhantomData,
        }
    }

    /// Splits the iterator at `index`, yielding two disjoint iterators.
    ///
    /// `index` is relative to the current state of the iterator (which is not
    /// necessarily the start of the axis).
    ///
    /// **Panics** if `index` is strictly greater than the iterator's remaining
    /// length.
    #[track_caller]
    pub fn split_at(self, index: usize) -> (Self, Self)
    {
        let (left, right) = self.iter.split_at(index);
        (
            AxisIter {
                iter: left,
                life: self.life,
            },
            AxisIter {
                iter: right,
                life: self.life,
            },
        )
    }
}

impl<'a, A, D> Iterator for AxisIter<'a, A, D>
where D: Dimension
{
    type Item = ArrayView<'a, A, D>;

    fn next(&mut self) -> Option<Self::Item>
    {
        self.iter.next().map(|ptr| unsafe { self.as_ref(ptr) })
    }

    fn size_hint(&self) -> (usize, Option<usize>)
    {
        self.iter.size_hint()
    }
}

impl<A, D> DoubleEndedIterator for AxisIter<'_, A, D>
where D: Dimension
{
    fn next_back(&mut self) -> Option<Self::Item>
    {
        self.iter.next_back().map(|ptr| unsafe { self.as_ref(ptr) })
    }
}

impl<A, D> ExactSizeIterator for AxisIter<'_, A, D>
where D: Dimension
{
    fn len(&self) -> usize
    {
        self.iter.len()
    }
}

/// An iterator that traverses over an axis and
/// and yields each subview (mutable)
///
/// The outermost dimension is `Axis(0)`, created with `.outer_iter()`,
/// but you can traverse arbitrary dimension with `.axis_iter()`.
///
/// For example, in a 3 × 5 × 5 array, with `axis` equal to `Axis(2)`,
/// the iterator element is a 3 × 5 subview (and there are 5 in total).
///
/// Iterator element type is `ArrayViewMut<'a, A, D>`.
///
/// See [`.outer_iter_mut()`](crate::ArrayRef::outer_iter_mut)
/// or [`.axis_iter_mut()`](crate::ArrayRef::axis_iter_mut)
/// for more information.
pub struct AxisIterMut<'a, A, D>
{
    iter: AxisIterCore<A, D>,
    life: PhantomData<&'a mut A>,
}

impl<'a, A, D: Dimension> AxisIterMut<'a, A, D>
{
    /// Creates a new iterator over the specified axis.
    pub(crate) fn new<Di>(v: ArrayViewMut<'a, A, Di>, axis: Axis) -> Self
    where Di: RemoveAxis<Smaller = D>
    {
        AxisIterMut {
            iter: AxisIterCore::new(v, axis),
            life: PhantomData,
        }
    }

    /// Splits the iterator at `index`, yielding two disjoint iterators.
    ///
    /// `index` is relative to the current state of the iterator (which is not
    /// necessarily the start of the axis).
    ///
    /// **Panics** if `index` is strictly greater than the iterator's remaining
    /// length.
    #[track_caller]
    pub fn split_at(self, index: usize) -> (Self, Self)
    {
        let (left, right) = self.iter.split_at(index);
        (
            AxisIterMut {
                iter: left,
                life: self.life,
            },
            AxisIterMut {
                iter: right,
                life: self.life,
            },
        )
    }
}

impl<'a, A, D> Iterator for AxisIterMut<'a, A, D>
where D: Dimension
{
    type Item = ArrayViewMut<'a, A, D>;

    fn next(&mut self) -> Option<Self::Item>
    {
        self.iter.next().map(|ptr| unsafe { self.as_ref(ptr) })
    }

    fn size_hint(&self) -> (usize, Option<usize>)
    {
        self.iter.size_hint()
    }
}

impl<A, D> DoubleEndedIterator for AxisIterMut<'_, A, D>
where D: Dimension
{
    fn next_back(&mut self) -> Option<Self::Item>
    {
        self.iter.next_back().map(|ptr| unsafe { self.as_ref(ptr) })
    }
}

impl<A, D> ExactSizeIterator for AxisIterMut<'_, A, D>
where D: Dimension
{
    fn len(&self) -> usize
    {
        self.iter.len()
    }
}

impl<A, D: Dimension> NdProducer for AxisIter<'_, A, D>
{
    type Item = <Self as Iterator>::Item;
    type Dim = Ix1;
    type Ptr = *mut A;
    type Stride = isize;

    fn layout(&self) -> crate::Layout
    {
        crate::Layout::one_dimensional()
    }

    fn raw_dim(&self) -> Self::Dim
    {
        Ix1(self.len())
    }

    fn as_ptr(&self) -> Self::Ptr
    {
        if self.len() > 0 {
            // `self.iter.index` is guaranteed to be in-bounds if any of the
            // iterator remains (i.e. if `self.len() > 0`).
            unsafe { self.iter.offset(self.iter.index) }
        } else {
            // In this case, `self.iter.index` may be past the end, so we must
            // not call `.offset()`. It's okay to return a dangling pointer
            // because it will never be used in the length 0 case.
            std::ptr::NonNull::dangling().as_ptr()
        }
    }

    fn contiguous_stride(&self) -> isize
    {
        self.iter.stride
    }

    unsafe fn as_ref(&self, ptr: Self::Ptr) -> Self::Item
    {
        ArrayView::new_(ptr, self.iter.inner_dim.clone(), self.iter.inner_strides.clone())
    }

    unsafe fn uget_ptr(&self, i: &Self::Dim) -> Self::Ptr
    {
        self.iter.offset(self.iter.index + i[0])
    }

    fn stride_of(&self, _axis: Axis) -> isize
    {
        self.contiguous_stride()
    }

    fn split_at(self, _axis: Axis, index: usize) -> (Self, Self)
    {
        self.split_at(index)
    }

    private_impl! {}
}

impl<A, D: Dimension> NdProducer for AxisIterMut<'_, A, D>
{
    type Item = <Self as Iterator>::Item;
    type Dim = Ix1;
    type Ptr = *mut A;
    type Stride = isize;

    fn layout(&self) -> crate::Layout
    {
        crate::Layout::one_dimensional()
    }

    fn raw_dim(&self) -> Self::Dim
    {
        Ix1(self.len())
    }

    fn as_ptr(&self) -> Self::Ptr
    {
        if self.len() > 0 {
            // `self.iter.index` is guaranteed to be in-bounds if any of the
            // iterator remains (i.e. if `self.len() > 0`).
            unsafe { self.iter.offset(self.iter.index) }
        } else {
            // In this case, `self.iter.index` may be past the end, so we must
            // not call `.offset()`. It's okay to return a dangling pointer
            // because it will never be used in the length 0 case.
            std::ptr::NonNull::dangling().as_ptr()
        }
    }

    fn contiguous_stride(&self) -> isize
    {
        self.iter.stride
    }

    unsafe fn as_ref(&self, ptr: Self::Ptr) -> Self::Item
    {
        ArrayViewMut::new_(ptr, self.iter.inner_dim.clone(), self.iter.inner_strides.clone())
    }

    unsafe fn uget_ptr(&self, i: &Self::Dim) -> Self::Ptr
    {
        self.iter.offset(self.iter.index + i[0])
    }

    fn stride_of(&self, _axis: Axis) -> isize
    {
        self.contiguous_stride()
    }

    fn split_at(self, _axis: Axis, index: usize) -> (Self, Self)
    {
        self.split_at(index)
    }

    private_impl! {}
}

/// An iterator that traverses over the specified axis
/// and yields views of the specified size on this axis.
///
/// For example, in a 2 × 8 × 3 array, if the axis of iteration
/// is 1 and the chunk size is 2, the yielded elements
/// are 2 × 2 × 3 views (and there are 4 in total).
///
/// Iterator element type is `ArrayView<'a, A, D>`.
///
/// See [`.axis_chunks_iter()`](crate::ArrayRef::axis_chunks_iter) for more information.
pub struct AxisChunksIter<'a, A, D>
{
    iter: AxisIterCore<A, D>,
    /// Index of the partial chunk (the chunk smaller than the specified chunk
    /// size due to the axis length not being evenly divisible). If the axis
    /// length is evenly divisible by the chunk size, this index is larger than
    /// the maximum valid index.
    partial_chunk_index: usize,
    /// Dimension of the partial chunk.
    partial_chunk_dim: D,
    life: PhantomData<&'a A>,
}

clone_bounds!(
    ['a, A, D: Clone]
    AxisChunksIter['a, A, D] {
        @copy {
            life,
            partial_chunk_index,
        }
        iter,
        partial_chunk_dim,
    }
);

/// Computes the information necessary to construct an iterator over chunks
/// along an axis, given a `view` of the array, the `axis` to iterate over, and
/// the chunk `size`.
///
/// Returns an axis iterator with the correct stride to move between chunks,
/// the number of chunks, and the shape of the last chunk.
///
/// **Panics** if `size == 0`.
#[track_caller]
fn chunk_iter_parts<A, D: Dimension>(v: ArrayView<'_, A, D>, axis: Axis, size: usize)
    -> (AxisIterCore<A, D>, usize, D)
{
    assert_ne!(size, 0, "Chunk size must be nonzero.");
    let axis_len = v.len_of(axis);
    let n_whole_chunks = axis_len / size;
    let chunk_remainder = axis_len % size;
    let iter_len = if chunk_remainder == 0 {
        n_whole_chunks
    } else {
        n_whole_chunks + 1
    };
    let stride = if n_whole_chunks == 0 {
        // This case avoids potential overflow when `size > axis_len`.
        0
    } else {
        v.stride_of(axis) * size as isize
    };

    let axis = axis.index();
    let mut inner_dim = v.dim.clone();
    inner_dim[axis] = size;

    let mut partial_chunk_dim = v.layout.dim;
    partial_chunk_dim[axis] = chunk_remainder;
    let partial_chunk_index = n_whole_chunks;

    let iter = AxisIterCore {
        index: 0,
        end: iter_len,
        stride,
        inner_dim,
        inner_strides: v.layout.strides,
        ptr: v.layout.ptr.as_ptr(),
    };

    (iter, partial_chunk_index, partial_chunk_dim)
}

impl<'a, A, D: Dimension> AxisChunksIter<'a, A, D>
{
    pub(crate) fn new(v: ArrayView<'a, A, D>, axis: Axis, size: usize) -> Self
    {
        let (iter, partial_chunk_index, partial_chunk_dim) = chunk_iter_parts(v, axis, size);
        AxisChunksIter {
            iter,
            partial_chunk_index,
            partial_chunk_dim,
            life: PhantomData,
        }
    }
}

macro_rules! chunk_iter_impl {
    ($iter:ident, $array:ident) => {
        impl<'a, A, D> $iter<'a, A, D>
        where
            D: Dimension,
        {
            fn get_subview(&self, index: usize, ptr: *mut A) -> $array<'a, A, D> {
                if index != self.partial_chunk_index {
                    unsafe {
                        $array::new_(
                            ptr,
                            self.iter.inner_dim.clone(),
                            self.iter.inner_strides.clone(),
                        )
                    }
                } else {
                    unsafe {
                        $array::new_(
                            ptr,
                            self.partial_chunk_dim.clone(),
                            self.iter.inner_strides.clone(),
                        )
                    }
                }
            }

            /// Splits the iterator at index, yielding two disjoint iterators.
            ///
            /// `index` is relative to the current state of the iterator (which is not
            /// necessarily the start of the axis).
            ///
            /// **Panics** if `index` is strictly greater than the iterator's remaining
            /// length.
            #[track_caller]
            pub fn split_at(self, index: usize) -> (Self, Self) {
                let (left, right) = self.iter.split_at(index);
                (
                    Self {
                        iter: left,
                        partial_chunk_index: self.partial_chunk_index,
                        partial_chunk_dim: self.partial_chunk_dim.clone(),
                        life: self.life,
                    },
                    Self {
                        iter: right,
                        partial_chunk_index: self.partial_chunk_index,
                        partial_chunk_dim: self.partial_chunk_dim,
                        life: self.life,
                    },
                )
            }
        }

        impl<'a, A, D> Iterator for $iter<'a, A, D>
        where
            D: Dimension,
        {
            type Item = $array<'a, A, D>;

            fn next(&mut self) -> Option<Self::Item> {
                self.iter
                    .next_with_index()
                    .map(|(index, ptr)| self.get_subview(index, ptr))
            }

            fn size_hint(&self) -> (usize, Option<usize>) {
                self.iter.size_hint()
            }
        }

        impl<'a, A, D> DoubleEndedIterator for $iter<'a, A, D>
        where
            D: Dimension,
        {
            fn next_back(&mut self) -> Option<Self::Item> {
                self.iter
                    .next_back_with_index()
                    .map(|(index, ptr)| self.get_subview(index, ptr))
            }
        }

        impl<'a, A, D> ExactSizeIterator for $iter<'a, A, D> where D: Dimension {}
    };
}

/// An iterator that traverses over the specified axis
/// and yields mutable views of the specified size on this axis.
///
/// For example, in a 2 × 8 × 3 array, if the axis of iteration
/// is 1 and the chunk size is 2, the yielded elements
/// are 2 × 2 × 3 views (and there are 4 in total).
///
/// Iterator element type is `ArrayViewMut<'a, A, D>`.
///
/// See [`.axis_chunks_iter_mut()`](crate::ArrayRef::axis_chunks_iter_mut)
/// for more information.
pub struct AxisChunksIterMut<'a, A, D>
{
    iter: AxisIterCore<A, D>,
    partial_chunk_index: usize,
    partial_chunk_dim: D,
    life: PhantomData<&'a mut A>,
}

impl<'a, A, D: Dimension> AxisChunksIterMut<'a, A, D>
{
    pub(crate) fn new(v: ArrayViewMut<'a, A, D>, axis: Axis, size: usize) -> Self
    {
        let (iter, partial_chunk_index, partial_chunk_dim) = chunk_iter_parts(v.into_view(), axis, size);
        AxisChunksIterMut {
            iter,
            partial_chunk_index,
            partial_chunk_dim,
            life: PhantomData,
        }
    }
}

chunk_iter_impl!(AxisChunksIter, ArrayView);
chunk_iter_impl!(AxisChunksIterMut, ArrayViewMut);

send_sync_read_only!(Iter);
send_sync_read_only!(IndexedIter);
send_sync_read_only!(LanesIter);
send_sync_read_only!(AxisIter);
send_sync_read_only!(AxisChunksIter);
send_sync_read_only!(ElementsBase);

send_sync_read_write!(IterMut);
send_sync_read_write!(IndexedIterMut);
send_sync_read_write!(LanesIterMut);
send_sync_read_write!(AxisIterMut);
send_sync_read_write!(AxisChunksIterMut);
send_sync_read_write!(ElementsBaseMut);

/// (Trait used internally) An iterator that we trust
/// to deliver exactly as many items as it said it would.
///
/// The iterator must produce exactly the number of elements it reported or
/// diverge before reaching the end.
#[allow(clippy::missing_safety_doc)] // not nameable downstream
pub unsafe trait TrustedIterator {}

use crate::indexes::IndicesIterF;
use crate::iter::IndicesIter;
#[cfg(feature = "std")]
use crate::{geomspace::Geomspace, linspace::Linspace, logspace::Logspace};
#[cfg(feature = "std")]
unsafe impl<F> TrustedIterator for Linspace<F> {}
#[cfg(feature = "std")]
unsafe impl<F> TrustedIterator for Geomspace<F> {}
#[cfg(feature = "std")]
unsafe impl<F> TrustedIterator for Logspace<F> {}
unsafe impl<A, D> TrustedIterator for Iter<'_, A, D> {}
unsafe impl<A, D> TrustedIterator for IterMut<'_, A, D> {}
unsafe impl<I> TrustedIterator for std::iter::Cloned<I> where I: TrustedIterator {}
unsafe impl<I, F> TrustedIterator for std::iter::Map<I, F> where I: TrustedIterator {}
unsafe impl<A> TrustedIterator for slice::Iter<'_, A> {}
unsafe impl<A> TrustedIterator for slice::IterMut<'_, A> {}
unsafe impl TrustedIterator for ::std::ops::Range<usize> {}
// FIXME: These indices iter are dubious -- size needs to be checked up front.
unsafe impl<D> TrustedIterator for IndicesIter<D> where D: Dimension {}
unsafe impl<D> TrustedIterator for IndicesIterF<D> where D: Dimension {}
unsafe impl<A, D> TrustedIterator for IntoIter<A, D> where D: Dimension {}

/// Like Iterator::collect, but only for trusted length iterators
pub fn to_vec<I>(iter: I) -> Vec<I::Item>
where I: TrustedIterator + ExactSizeIterator
{
    to_vec_mapped(iter, |x| x)
}

/// Like Iterator::collect, but only for trusted length iterators
pub fn to_vec_mapped<I, F, B>(iter: I, mut f: F) -> Vec<B>
where
    I: TrustedIterator + ExactSizeIterator,
    F: FnMut(I::Item) -> B,
{
    // Use an `unsafe` block to do this efficiently.
    // We know that iter will produce exactly .size() elements,
    // and the loop can vectorize if it's clean (without branch to grow the vector).
    let (size, _) = iter.size_hint();
    let mut result = Vec::with_capacity(size);
    let mut out_ptr = result.as_mut_ptr();
    let mut len = 0;
    iter.fold((), |(), elt| unsafe {
        ptr::write(out_ptr, f(elt));
        len += 1;
        result.set_len(len);
        out_ptr = out_ptr.offset(1);
    });
    debug_assert_eq!(size, result.len());
    result
}