Fix to_shared to avoid cloning when it is already ArcArray

src/data_traits.rs

@@ -96,6 +96,18 @@ pub unsafe trait Data: RawData {
     where
         Self::Elem: Clone,
         D: Dimension;
+
+    /// Return a shared ownership (copy on write) array based on the existing one,
+    /// cloning elements if necessary.
+    #[doc(hidden)]
+    fn to_shared<D>(self_: &ArrayBase<Self, D>) -> ArrayBase<OwnedArcRepr<Self::Elem>, D>
+    where
+        Self::Elem: Clone,
+        D: Dimension,
+    {
+        // clone to shared
+        self_.to_owned().into_shared()
+    }
 }
 
 /// Array representation trait.
@@ -238,6 +250,15 @@ unsafe impl<A> Data for OwnedArcRepr<A> {
             strides: self_.strides,
         }
     }
+
+    fn to_shared<D>(self_: &ArrayBase<Self, D>) -> ArrayBase<OwnedArcRepr<Self::Elem>, D>
+    where
+        Self::Elem: Clone,
+        D: Dimension,
+    {
+        // to shared using clone of OwnedArcRepr without clone of raw data.
+        self_.clone()
+    }
 }
 
 unsafe impl<A> DataMut for OwnedArcRepr<A> where A: Clone {}

src/impl_methods.rs

@@ -214,14 +214,14 @@ where
         }
     }
 
-    /// Return a shared ownership (copy on write) array.
+    /// Return a shared ownership (copy on write) array, cloning the array
+    /// elements if necessary.
     pub fn to_shared(&self) -> ArcArray<A, D>
     where
         A: Clone,
         S: Data,
     {
-        // FIXME: Avoid copying if it’s already an ArcArray.
-        self.to_owned().into_shared()
+        S::to_shared(self)
     }
 
     /// Turn the array into a uniquely owned array, cloning the array elements