Avoid re-borrowing in multislice! macro

The old implementation always called `.view_mut()` on the input array,
which meant that it was not possible to use `multislice!` to split an
`ArrayViewMut` instance into pieces with the same lifetime as the
original view. Now, `multislice!` uses `ArrayViewMut::from()` instead
so that this works. The primary disadvantage is that an explicit
borrow is necessary in many cases, which is less concise.

Closes #687.

Author: jturner314

src/lib.rs

@@ -524,7 +524,7 @@ pub type Ixs = isize;
 /// // - 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) = multislice!(h, mut [.., ..;2], mut [.., 1..;2]);
+/// let (s0, s1) = multislice!(&mut h, mut [.., ..;2], mut [.., 1..;2]);
 /// let i = arr2(&[[0, 2],
 ///                [4, 6]]);
 /// let j = arr2(&[[1, 3],

src/slice.rs

@@ -657,8 +657,8 @@ pub unsafe fn deref_raw_view_mut_into_view_mut_with_life<'a, A, D: Dimension>(
 /// disjoint).
 ///
 /// The syntax is `multislice!(` *expression, pattern [, pattern [, …]]* `)`,
-/// where *expression* evaluates to a mutable array, and each *pattern* is
-/// either
+/// where *expression* is any valid input to `ArrayViewMut::from()`, and each
+/// *pattern* is either
 ///
 /// * `mut` *s-args-or-expr*: creates an `ArrayViewMut` or
 /// * *s-args-or-expr*: creates an `ArrayView`
@@ -667,9 +667,9 @@ pub unsafe fn deref_raw_view_mut_into_view_mut_with_life<'a, A, D: Dimension>(
 /// the [`s!`] macro to create a `&SliceInfo` instance or (2) an expression
 /// that evaluates to a `&SliceInfo` instance.
 ///
-/// **Note** that this macro always mutably borrows the array even if there are
-/// no `mut` patterns. If all you want to do is take read-only slices, you
-/// don't need `multislice!()`; just call
+/// **Note** that *expression* is converted to an `ArrayViewMut` using
+/// `ArrayViewMut::from()` even if there are no `mut` patterns. If all you want
+/// to do is take read-only slices, you don't need `multislice!()`; just call
 /// [`.slice()`](struct.ArrayBase.html#method.slice) multiple times instead.
 ///
 /// `multislice!()` evaluates to a tuple of `ArrayView` and/or `ArrayViewMut`
@@ -697,7 +697,7 @@ pub unsafe fn deref_raw_view_mut_into_view_mut_with_life<'a, A, D: Dimension>(
 ///
 /// # fn main() {
 /// let mut arr: Array1<_> = (0..12).collect();
-/// let (a, b, c, d) = multislice!(arr, [0..5], mut [6..;2], [1..6], mut [7..;2]);
+/// let (a, b, c, d) = multislice!(&mut arr, [0..5], mut [6..;2], [1..6], mut [7..;2]);
 /// assert_eq!(a, array![0, 1, 2, 3, 4]);
 /// assert_eq!(b, array![6, 8, 10]);
 /// assert_eq!(c, array![1, 2, 3, 4, 5]);
@@ -715,7 +715,7 @@ pub unsafe fn deref_raw_view_mut_into_view_mut_with_life<'a, A, D: Dimension>(
 ///   # use ndarray::prelude::*;
 ///   # fn main() {
 ///   let mut arr: Array1<_> = (0..12).collect();
-///   multislice!(arr, [0..5], mut [1..;2]); // panic!
+///   multislice!(&mut arr, [0..5], mut [1..;2]); // panic!
 ///   # }
 ///   ```
 ///
@@ -727,7 +727,7 @@ pub unsafe fn deref_raw_view_mut_into_view_mut_with_life<'a, A, D: Dimension>(
 ///   # use ndarray::prelude::*;
 ///   # fn main() {
 ///   let mut arr: Array1<_> = (0..12).collect();
-///   multislice!(arr, mut [0..5], mut [1..;2]); // panic!
+///   multislice!(&mut arr, mut [0..5], mut [1..;2]); // panic!
 ///   # }
 ///   ```
 #[macro_export]
@@ -985,7 +985,7 @@ macro_rules! multislice(
     ($arr:expr, $($t:tt)*) => {
         {
             let (life, raw_view) = {
-                let mut view = $crate::ArrayBase::view_mut(&mut $arr);
+                let mut view: $crate::ArrayViewMut<_, _> = ::core::convert::From::from($arr);
                 ($crate::life_of_view_mut(&view), view.raw_view_mut())
             };
             $crate::multislice!(@parse raw_view, life, (), (), (), ($($t)*))

tests/array.rs

@@ -336,76 +336,76 @@ fn test_slice_collapse_with_indices() {
 }
 
 #[test]
-#[allow(clippy::cognitive_complexity)]
 fn test_multislice() {
-    defmac!(test_multislice mut arr, s1, s2 => {
-        {
-            let copy = arr.clone();
-            assert_eq!(
-                multislice!(arr, mut s1, mut s2,),
-                (copy.clone().slice_mut(s1), copy.clone().slice_mut(s2))
-            );
-        }
-        {
-            let copy = arr.clone();
-            assert_eq!(
-                multislice!(arr, mut s1, s2,),
-                (copy.clone().slice_mut(s1), copy.clone().slice(s2))
-            );
-        }
-        {
-            let copy = arr.clone();
-            assert_eq!(
-                multislice!(arr, s1, mut s2),
-                (copy.clone().slice(s1), copy.clone().slice_mut(s2))
-            );
-        }
-        {
-            let copy = arr.clone();
-            assert_eq!(
-                multislice!(arr, s1, s2),
-                (copy.clone().slice(s1), copy.clone().slice(s2))
-            );
-        }
-    });
+    macro_rules! check_multislice {
+        ($arr:expr, $s1:expr, $s2:expr) => {
+            {
+                let copy = $arr.clone();
+                assert_eq!(
+                    multislice!(&mut $arr, mut $s1, mut $s2,),
+                    (copy.clone().slice_mut($s1), copy.clone().slice_mut($s2))
+                );
+            }
+            {
+                let copy = $arr.clone();
+                assert_eq!(
+                    multislice!(&mut $arr, mut $s1, $s2,),
+                    (copy.clone().slice_mut($s1), copy.clone().slice($s2))
+                );
+            }
+            {
+                let copy = $arr.clone();
+                assert_eq!(
+                    multislice!(&mut $arr, $s1, mut $s2),
+                    (copy.clone().slice($s1), copy.clone().slice_mut($s2))
+                );
+            }
+            {
+                let copy = $arr.clone();
+                assert_eq!(
+                    multislice!(&mut $arr, $s1, $s2),
+                    (copy.clone().slice($s1), copy.clone().slice($s2))
+                );
+            }
+        };
+    };
     let mut arr = Array1::from_iter(0..48).into_shape((8, 6)).unwrap();
-
-    assert_eq!((arr.clone().view(),), multislice!(arr, [.., ..]));
-    test_multislice!(&mut arr, s![0, ..], s![1, ..]);
-    test_multislice!(&mut arr, s![0, ..], s![-1, ..]);
-    test_multislice!(&mut arr, s![0, ..], s![1.., ..]);
-    test_multislice!(&mut arr, s![1, ..], s![..;2, ..]);
-    test_multislice!(&mut arr, s![..2, ..], s![2.., ..]);
-    test_multislice!(&mut arr, s![1..;2, ..], s![..;2, ..]);
-    test_multislice!(&mut arr, s![..;-2, ..], s![..;2, ..]);
-    test_multislice!(&mut arr, s![..;12, ..], s![3..;3, ..]);
+    assert_eq!((arr.clone().view(),), multislice!(&mut arr, [.., ..]));
+    check_multislice!(arr, s![0, ..], s![1, ..]);
+    check_multislice!(arr, s![0, ..], s![-1, ..]);
+    check_multislice!(arr, s![0, ..], s![1.., ..]);
+    check_multislice!(arr, s![1, ..], s![..;2, ..]);
+    check_multislice!(arr, s![..2, ..], s![2.., ..]);
+    check_multislice!(arr, s![1..;2, ..], s![..;2, ..]);
+    check_multislice!(arr, s![..;-2, ..], s![..;2, ..]);
+    check_multislice!(arr, s![..;12, ..], s![3..;3, ..]);
 }
 
 #[test]
 fn test_multislice_intersecting() {
     assert_panics!({
         let mut arr = Array2::<u8>::zeros((8, 6));
-        multislice!(arr, mut [3, ..], [3, ..]);
+        multislice!(&mut arr, mut [3, ..], [3, ..]);
     });
     assert_panics!({
         let mut arr = Array2::<u8>::zeros((8, 6));
-        multislice!(arr, mut [3, ..], [3.., ..]);
+        multislice!(&mut arr, mut [3, ..], [3.., ..]);
     });
     assert_panics!({
         let mut arr = Array2::<u8>::zeros((8, 6));
-        multislice!(arr, mut [3, ..], [..;3, ..]);
+        multislice!(&mut arr, mut [3, ..], [..;3, ..]);
     });
     assert_panics!({
         let mut arr = Array2::<u8>::zeros((8, 6));
-        multislice!(arr, mut [..;6, ..], [3..;3, ..]);
+        multislice!(&mut arr, mut [..;6, ..], [3..;3, ..]);
     });
     assert_panics!({
         let mut arr = Array2::<u8>::zeros((8, 6));
-        multislice!(arr, mut [2, ..], mut [..-1;-2, ..]);
+        multislice!(&mut arr, mut [2, ..], mut [..-1;-2, ..]);
     });
     {
         let mut arr = Array2::<u8>::zeros((8, 6));
-        multislice!(arr, [3, ..], [-1..;-2, ..]);
+        multislice!(&mut arr, [3, ..], [-1..;-2, ..]);
     }
 }
 
@@ -418,7 +418,7 @@ fn test_multislice_eval_args_only_once() {
             eval_count += 1;
             *s![1..2]
         };
-        multislice!(arr, mut &slice(), [3..4], [5..6]);
+        multislice!(&mut arr, mut &slice(), [3..4], [5..6]);
     }
     assert_eq!(eval_count, 1);
     let mut eval_count = 0;
@@ -427,7 +427,7 @@ fn test_multislice_eval_args_only_once() {
             eval_count += 1;
             *s![1..2]
         };
-        multislice!(arr, [3..4], mut &slice(), [5..6]);
+        multislice!(&mut arr, [3..4], mut &slice(), [5..6]);
     }
     assert_eq!(eval_count, 1);
     let mut eval_count = 0;
@@ -436,7 +436,7 @@ fn test_multislice_eval_args_only_once() {
             eval_count += 1;
             *s![1..2]
         };
-        multislice!(arr, [3..4], [5..6], mut &slice());
+        multislice!(&mut arr, [3..4], [5..6], mut &slice());
     }
     assert_eq!(eval_count, 1);
     let mut eval_count = 0;
@@ -445,7 +445,7 @@ fn test_multislice_eval_args_only_once() {
             eval_count += 1;
             *s![1..2]
         };
-        multislice!(arr, &slice(), mut [3..4], [5..6]);
+        multislice!(&mut arr, &slice(), mut [3..4], [5..6]);
     }
     assert_eq!(eval_count, 1);
     let mut eval_count = 0;
@@ -454,7 +454,7 @@ fn test_multislice_eval_args_only_once() {
             eval_count += 1;
             *s![1..2]
         };
-        multislice!(arr, mut [3..4], &slice(), [5..6]);
+        multislice!(&mut arr, mut [3..4], &slice(), [5..6]);
     }
     assert_eq!(eval_count, 1);
     let mut eval_count = 0;
@@ -463,11 +463,33 @@ fn test_multislice_eval_args_only_once() {
             eval_count += 1;
             *s![1..2]
         };
-        multislice!(arr, mut [3..4], [5..6], &slice());
+        multislice!(&mut arr, mut [3..4], [5..6], &slice());
     }
     assert_eq!(eval_count, 1);
 }
 
+#[test]
+fn test_multislice_arrayviewmut_same_life() {
+    // This test makes sure that it's possible for the borrowed elements
+    // returned from `get_mut2` to have the same life as the `arr` view.
+    fn get_mut2<'a, A>(
+        arr: ArrayViewMut<'a, A, Ix2>,
+        [i1, j1]: [usize; 2],
+        [i2, j2]: [usize; 2],
+    ) -> (&'a mut A, &'a mut A) {
+        use ndarray::IndexLonger;
+        let (x1, x2) = multislice!(arr, mut [i1, j1], mut [i2, j2]);
+        (x1.index([]), x2.index([]))
+    }
+    let mut arr = array![[1, 2], [3, 4]];
+    {
+        let (x1, x2) = get_mut2(arr.view_mut(), [0, 0], [1, 0]);
+        *x1 += 1;
+        *x2 += 2;
+    }
+    assert_eq!(arr, array![[2, 2], [5, 4]]);
+}
+
 #[should_panic]
 #[test]
 fn index_out_of_bounds() {