Add is_unique for ArcArray (#1399)

Author: daniellga

src/impl_arc_array.rs

@@ -0,0 +1,25 @@
+// Copyright 2019 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.
+
+use crate::imp_prelude::*;
+use alloc::sync::Arc;
+
+/// Methods specific to `ArcArray`.
+///
+/// ***See also all methods for [`ArrayBase`]***
+impl<A, D> ArcArray<A, D>
+where D: Dimension
+{
+    /// Returns `true` iff the inner `Arc` is not shared.
+    /// If you want to ensure the `Arc` is not concurrently cloned, you need to provide a `&mut self` to this function.
+    pub fn is_unique(&self) -> bool
+    {
+        // Only strong pointers are used in this crate.
+        Arc::strong_count(&self.data.0) == 1
+    }
+}

src/lib.rs

@@ -1612,6 +1612,9 @@ mod impl_raw_views;
 // Copy-on-write array methods
 mod impl_cow;
 
+// Arc array methods
+mod impl_arc_array;
+
 /// Returns `true` if the pointer is aligned.
 pub(crate) fn is_aligned<T>(ptr: *const T) -> bool
 {