rust-ndarray · jturner314 · Sep 18, 2019 · Sep 19, 2019
diff --git a/src/dimension/mod.rs b/src/dimension/mod.rs
@@ -545,7 +545,6 @@ fn slice_min_max(axis_len: usize, slice: Slice) -> Option<(usize, usize)> {
 }
 
 /// Returns `true` iff the slices intersect.
-#[allow(dead_code)]
 pub fn slices_intersect<D: Dimension>(
     dim: &D,
     indices1: &D::SliceArg,

diff --git a/src/impl_methods.rs b/src/impl_methods.rs
@@ -28,6 +28,7 @@ use crate::iter::{
     AxisChunksIter, AxisChunksIterMut, AxisIter, AxisIterMut, ExactChunks, ExactChunksMut,
     IndexedIter, IndexedIterMut, Iter, IterMut, Lanes, LanesMut, Windows,
 };
+use crate::slice::MultiSlice;
 use crate::stacking::stack;
 use crate::{NdIndex, Slice, SliceInfo, SliceOrIndex};
 
@@ -350,6 +351,39 @@ where
         self.view_mut().slice_move(info)
     }
 
+    /// Return multiple disjoint, sliced, mutable views of the array.
+    ///
+    /// See [*Slicing*](#slicing) for full documentation.
+    /// See also [`SliceInfo`] and [`D::SliceArg`].
+    ///
+    /// [`SliceInfo`]: struct.SliceInfo.html
+    /// [`D::SliceArg`]: trait.Dimension.html#associatedtype.SliceArg
+    ///
+    /// **Panics** if any of the following occur:
+    ///
+    /// * if any of the views would intersect (i.e. if any element would appear in multiple slices)
+    /// * if an index is out of bounds or step size is zero
+    /// * if `D` is `IxDyn` and `info` does not match the number of array axes
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use ndarray::{arr2, s};
+    ///
+    /// let mut a = arr2(&[[1, 2, 3], [4, 5, 6]]);
+    /// let (mut edges, mut middle) = a.multi_slice_mut((s![.., ..;2], s![.., 1]));
+    /// edges.fill(1);
+    /// middle.fill(0);
+    /// assert_eq!(a, arr2(&[[1, 0, 1], [1, 0, 1]]));
+    /// ```
+    pub fn multi_slice_mut<'a, M>(&'a mut self, info: M) -> M::Output
+    where
+        M: MultiSlice<'a, A, D>,
+        S: DataMut,
+    {
+        unsafe { info.slice_and_deref(self.raw_view_mut()) }
+    }
+
     /// Slice the array, possibly changing the number of dimensions.
     ///
     /// See [*Slicing*](#slicing) for full documentation.

diff --git a/src/impl_views/splitting.rs b/src/impl_views/splitting.rs
@@ -7,6 +7,7 @@
 // except according to those terms.
 
 use crate::imp_prelude::*;
+use crate::slice::MultiSlice;
 
 /// Methods for read-only array views.
 impl<'a, A, D> ArrayView<'a, A, D>
@@ -109,4 +110,29 @@ where
             (left.deref_into_view_mut(), right.deref_into_view_mut())
         }
     }
+
+    /// Split the view into multiple disjoint slices.
+    ///
+    /// This is similar to [`.multi_slice_mut()`], but `.multi_slice_move()`
+    /// consumes `self` and produces views with lifetimes matching that of
+    /// `self`.
+    ///
+    /// See [*Slicing*](#slicing) for full documentation.
+    /// See also [`SliceInfo`] and [`D::SliceArg`].
+    ///
+    /// [`.multi_slice_mut()`]: struct.ArrayBase.html#method.multi_slice_mut
+    /// [`SliceInfo`]: struct.SliceInfo.html
+    /// [`D::SliceArg`]: trait.Dimension.html#associatedtype.SliceArg
+    ///
+    /// **Panics** if any of the following occur:
+    ///
+    /// * if any of the views would intersect (i.e. if any element would appear in multiple slices)
+    /// * if an index is out of bounds or step size is zero
+    /// * if `D` is `IxDyn` and `info` does not match the number of array axes
+    pub fn multi_slice_move<M>(mut self, info: M) -> M::Output
+    where
+        M: MultiSlice<'a, A, D>,
+    {
+        unsafe { info.slice_and_deref(self.raw_view_mut()) }
+    }
 }
diff --git a/src/lib.rs b/src/lib.rs
@@ -473,6 +473,13 @@ pub type Ixs = isize;
 /// [`.slice_move()`]: #method.slice_move
 /// [`.slice_collapse()`]: #method.slice_collapse
 ///
+/// It's possible to take multiple simultaneous *mutable* slices with the
+/// [`.multi_slice_mut()`] or (for [`ArrayViewMut`] only)
+/// [`.multi_slice_move()`].
+///
+/// [`.multi_slice_mut()`]: #method.multi_slice_mut
+/// [`.multi_slice_move()`]: type.ArrayViewMut.html#method.multi_slice_move
+///
 /// ```
 /// extern crate ndarray;
 ///
@@ -523,6 +530,20 @@ pub type Ixs = isize;
 ///                [12, 11, 10]]);
 /// assert_eq!(f, g);
 /// assert_eq!(f.shape(), &[2, 3]);
+///
+/// // Let's take two disjoint, mutable slices of a matrix with
+/// //
+/// // - One containing all the even-index columns in the matrix
+/// // - One containing all the odd-index columns in the matrix
+/// let mut h = arr2(&[[0, 1, 2, 3],
+///                    [4, 5, 6, 7]]);
+/// let (s0, s1) = h.multi_slice_mut((s![.., ..;2], s![.., 1..;2]));
+/// let i = arr2(&[[0, 2],
+///                [4, 6]]);
+/// let j = arr2(&[[1, 3],
+///                [5, 7]]);
+/// assert_eq!(s0, i);
+/// assert_eq!(s1, j);
 /// }
 /// ```
 ///

diff --git a/src/slice.rs b/src/slice.rs
@@ -5,8 +5,9 @@
 // <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.
+use crate::dimension::slices_intersect;
 use crate::error::{ErrorKind, ShapeError};
-use crate::Dimension;
+use crate::{ArrayViewMut, Dimension, RawArrayViewMut};
 use std::fmt;
 use std::marker::PhantomData;
 use std::ops::{Deref, Range, RangeFrom, RangeFull, RangeInclusive, RangeTo, RangeToInclusive};
@@ -629,3 +630,189 @@ macro_rules! s(
         &*&$crate::s![@parse ::std::marker::PhantomData::<$crate::Ix0>, [] $($t)*]
     };
 );
+
+/// Slicing information describing multiple mutable, disjoint slices.
+///
+/// It's unfortunate that we need `'out` and `A` to be parameters of the trait,
+/// but they're necessary until Rust supports generic associated types.
+///
+/// # Safety
+///
+/// Implementers of this trait must ensure that:
+///
+/// * `.slice_and_deref()` panics or aborts if the slices would intersect, and
+///
+/// * the `.intersects_self()`, `.intersects_indices()`, and
+///   `.intersects_other()` implementations are correct.
+pub unsafe trait MultiSlice<'out, A, D>
+where
+    A: 'out,
+    D: Dimension,
+{
+    /// The type of the slices created by `.slice_and_deref()`.
+    type Output;
+
+    /// Slice the raw view into multiple raw views, and dereference them.
+    ///
+    /// **Panics** if performing any individual slice panics or if the slices
+    /// are not disjoint (i.e. if they intersect).
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that it is safe to mutably dereference the view
+    /// using the lifetime `'out`.
+    unsafe fn slice_and_deref(&self, view: RawArrayViewMut<A, D>) -> Self::Output;
+
+    /// Returns `true` if slicing an array of the specified `shape` with `self`
+    /// would result in intersecting slices.
+    ///
+    /// If `self.intersects_self(&view.raw_dim())` is `true`, then
+    /// `self.slice_and_deref(view)` must panic.
+    fn intersects_self(&self, shape: &D) -> bool;
+
+    /// Returns `true` if any slices created by slicing an array of the
+    /// specified `shape` with `self` would intersect with the specified
+    /// indices.
+    ///
+    /// Note that even if this returns `false`, `self.intersects_self(shape)`
+    /// may still return `true`. (`.intersects_indices()` doesn't check for
+    /// intersections within `self`; it only checks for intersections between
+    /// `self` and `indices`.)
+    fn intersects_indices(&self, shape: &D, indices: &D::SliceArg) -> bool;
+
+    /// Returns `true` if any slices created by slicing an array of the
+    /// specified `shape` with `self` would intersect any slices created by
+    /// slicing the array with `other`.
+    ///
+    /// Note that even if this returns `false`, `self.intersects_self(shape)`
+    /// or `other.intersects_self(shape)` may still return `true`.
+    /// (`.intersects_other()` doesn't check for intersections within `self` or
+    /// within `other`; it only checks for intersections between `self` and
+    /// `other`.)
+    fn intersects_other(&self, shape: &D, other: impl MultiSlice<'out, A, D>) -> bool;
+}
+
+unsafe impl<'out, A, D, Do> MultiSlice<'out, A, D> for SliceInfo<D::SliceArg, Do>
+where
+    A: 'out,
+    D: Dimension,
+    Do: Dimension,
+{
+    type Output = ArrayViewMut<'out, A, Do>;
+
+    unsafe fn slice_and_deref(&self, view: RawArrayViewMut<A, D>) -> Self::Output {
+        view.slice_move(self).deref_into_view_mut()
+    }
+
+    fn intersects_self(&self, _shape: &D) -> bool {
+        false
+    }
+
+    fn intersects_indices(&self, shape: &D, indices: &D::SliceArg) -> bool {
+        slices_intersect(shape, &*self, indices)
+    }
+
+    fn intersects_other(&self, shape: &D, other: impl MultiSlice<'out, A, D>) -> bool {
+        other.intersects_indices(shape, &*self)
+    }
+}
+
+unsafe impl<'out, A, D> MultiSlice<'out, A, D> for ()
+where
+    A: 'out,
+    D: Dimension,
+{
+    type Output = ();
+
+    unsafe fn slice_and_deref(&self, _view: RawArrayViewMut<A, D>) -> Self::Output {}
+
+    fn intersects_self(&self, _shape: &D) -> bool {
+        false
+    }
+
+    fn intersects_indices(&self, _shape: &D, _indices: &D::SliceArg) -> bool {
+        false
+    }
+
+    fn intersects_other(&self, _shape: &D, _other: impl MultiSlice<'out, A, D>) -> bool {
+        false
+    }
+}
+
+macro_rules! impl_multislice_tuple {
+    ($($T:ident,)*) => {
+        unsafe impl<'out, A, D, $($T,)*> MultiSlice<'out, A, D> for ($($T,)*)
+        where
+            A: 'out,
+            D: Dimension,
+            $($T: MultiSlice<'out, A, D>,)*
+        {
+            type Output = ($($T::Output,)*);
+
+            unsafe fn slice_and_deref(&self, view: RawArrayViewMut<A, D>) -> Self::Output {
+                assert!(!self.intersects_self(&view.raw_dim()));
+
+                #[allow(non_snake_case)]
+                let ($($T,)*) = self;
+                ($($T.slice_and_deref(view.clone()),)*)
+            }
+
+            fn intersects_self(&self, shape: &D) -> bool {
+                #[allow(non_snake_case)]
+                let ($($T,)*) = self;
+                impl_multislice_tuple!(@intersects_self shape, ($($T,)*))
+            }
+
+            fn intersects_indices(&self, shape: &D, indices: &D::SliceArg) -> bool {
+                #[allow(non_snake_case)]
+                let ($($T,)*) = self;
+                $($T.intersects_indices(shape, indices)) ||*
+            }
+
+            fn intersects_other(&self, shape: &D, other: impl MultiSlice<'out, A, D>) -> bool {
+                #[allow(non_snake_case)]
+                let ($($T,)*) = self;
+                $($T.intersects_other(shape, &other)) ||*
+            }
+        }
+    };
+    (@intersects_self $shape:expr, ($head:expr,)) => {
+        $head.intersects_self($shape)
+    };
+    (@intersects_self $shape:expr, ($head:expr, $($tail:expr,)*)) => {
+        $head.intersects_self($shape) ||
+            $($head.intersects_other($shape, &$tail)) ||* ||
+            impl_multislice_tuple!(@intersects_self $shape, ($($tail,)*))
+    };
+}
+impl_multislice_tuple!(T0,);
+impl_multislice_tuple!(T0, T1,);
+impl_multislice_tuple!(T0, T1, T2,);
+impl_multislice_tuple!(T0, T1, T2, T3,);
+impl_multislice_tuple!(T0, T1, T2, T3, T4,);
+impl_multislice_tuple!(T0, T1, T2, T3, T4, T5,);
+
+unsafe impl<'out, A, D, T> MultiSlice<'out, A, D> for &'_ T
+where
+    A: 'out,
+    D: Dimension,
+    T: MultiSlice<'out, A, D>,
+{
+    type Output = T::Output;
+
+    unsafe fn slice_and_deref(&self, view: RawArrayViewMut<A, D>) -> Self::Output {
+        T::slice_and_deref(self, view)
+    }
+
+    fn intersects_self(&self, shape: &D) -> bool {
+        T::intersects_self(self, shape)
+    }
+
+    fn intersects_indices(&self, shape: &D, indices: &D::SliceArg) -> bool {
+        T::intersects_indices(self, shape, indices)
+    }
+
+    fn intersects_other(&self, shape: &D, other: impl MultiSlice<'out, A, D>) -> bool {
+        T::intersects_other(self, shape, other)
+    }
+}