move_into: Add conversion .into_maybe_uninit() for array views

Author: bluss

src/impl_owned_array.rs

@@ -168,6 +168,27 @@ impl<A, D> Array<A, D>
     /// drop of any such element, other elements may be leaked.
     ///
     /// ***Panics*** if the shapes don't agree.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// use ndarray::Array;
+    ///
+    /// // Usage example of move_into in safe code
+    /// let mut a = Array::zeros((10, 10));
+    /// let b = Array::from_iter(0..100).into_shape((10, 10)).unwrap();
+    /// // make an MaybeUninit view so that we can *overwrite* into it.
+    /// b.move_into(a.view_mut().into_maybe_uninit());
+    ///
+    /// // Usage example using uninit
+    /// let mut a = Array::uninit((10, 10));
+    /// let b = Array::from_iter(0..100).into_shape((10, 10)).unwrap();
+    /// b.move_into(&mut a);
+    /// unsafe {
+    ///     // we can now promise we have fully initialized `a`.
+    ///     let a = a.assume_init();
+    /// }
+    /// ```
     pub fn move_into<'a, AM>(self, new_array: AM)
     where
         AM: Into<ArrayViewMut<'a, MaybeUninit<A>, D>>,

src/impl_views/conversions.rs

@@ -7,6 +7,7 @@
 // except according to those terms.
 
 use alloc::slice;
+use std::mem::MaybeUninit;
 
 use crate::imp_prelude::*;
 
@@ -133,6 +134,21 @@ where
             self.into_raw_view_mut().cast::<MathCell<A>>().deref_into_view()
         }
     }
+
+    /// Return the array view as a view of `MaybeUninit<A>` elements
+    ///
+    /// This conversion leaves the elements as they were (presumably initialized), but
+    /// they are represented with the `MaybeUninit<A>` type. Effectively this means that
+    /// the elements can be overwritten without dropping the old element in its place.
+    /// (In some situations this is not what you want, while for `Copy` elements it makes
+    /// no difference at all.)
+    pub fn into_maybe_uninit(self) -> ArrayViewMut<'a, MaybeUninit<A>, D> {
+        // Safe because: A and MaybeUninit<A> have the same representation;
+        // and we can go from initialized to (maybe) not unconditionally.
+        unsafe {
+            self.into_raw_view_mut().cast::<MaybeUninit<A>>().deref_into_view_mut()
+        }
+    }
 }
 
 /// Private array view methods