FEAT: Add methods .cell_view() and .into_cell_view()

Author: bluss

src/impl_methods.rs

@@ -6,6 +6,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use std::cell::Cell;
 use std::ptr as std_ptr;
 use std::slice;
 
@@ -151,6 +152,20 @@ where
         unsafe { ArrayViewMut::new(self.ptr, self.dim.clone(), self.strides.clone()) }
     }
 
+    /// Return a shared view of the array with elements as if they were embedded in cells.
+    ///
+    /// The cell view requires a mutable borrow of the array. Once borrowed the
+    /// cell view itself can be copied and accessed without exclusivity.
+    ///
+    /// The view acts "as if" the elements are temporarily in cells, and elements
+    /// can be changed through shared references using the regular cell methods.
+    pub fn cell_view(&mut self) -> ArrayView<'_, Cell<A>, D>
+    where
+        S: DataMut,
+    {
+        self.view_mut().into_cell_view()
+    }
+
     /// Return an uniquely owned copy of the array.
     ///
     /// If the input array is contiguous and its strides are positive, then the

src/impl_views/conversions.rs

@@ -6,6 +6,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use std::cell::Cell;
 use std::slice;
 
 use crate::imp_prelude::*;
@@ -117,6 +118,21 @@ where
     pub fn into_slice(self) -> Option<&'a mut [A]> {
         self.try_into_slice().ok()
     }
+
+    /// Return a shared view of the array with elements as if they were embedded in cells.
+    ///
+    /// The cell view itself can be copied and accessed without exclusivity.
+    ///
+    /// The view acts "as if" the elements are temporarily in cells, and elements
+    /// can be changed through shared references using the regular cell methods.
+    pub fn into_cell_view(self) -> ArrayView<'a, Cell<A>, D> {
+        // safety: valid because
+        // A and Cell<A> have the same representation
+        // &'a mut T is interchangeable with &'a Cell<T> -- see method Cell::from_mut
+        unsafe {
+            self.into_raw_view_mut().cast::<Cell<A>>().deref_into_view()
+        }
+    }
 }
 
 /// Private array view methods

tests/views.rs

@@ -0,0 +1,16 @@
+use ndarray::prelude::*;
+use ndarray::Zip;
+
+#[test]
+fn cell_view() {
+    let mut a = Array::from_shape_fn((10, 5), |(i, j)| (i * j) as f32);
+    let answer = &a + 1.;
+
+    {
+        let cv1 = a.cell_view();
+        let cv2 = cv1;
+
+        Zip::from(cv1).and(cv2).apply(|a, b| a.set(b.get() + 1.));
+    }
+    assert_eq!(a, answer);
+}