FEAT: Implement internal Array::maybe_uninit and assume_init

Use MaybeUninit to handle uninitialized data safely.

Author: bluss

src/impl_constructors.rs

@@ -13,6 +13,7 @@
 #![allow(clippy::match_wild_err_arm)]
 
 use num_traits::{Float, One, Zero};
+use std::mem::MaybeUninit;
 
 use crate::dimension;
 use crate::error::{self, ShapeError};
@@ -517,3 +518,22 @@ where
         Self::from_shape_vec_unchecked(shape, v)
     }
 }
+
+impl<S, A, D> ArrayBase<S, D>
+where
+    S: DataOwned<Elem = MaybeUninit<A>>,
+    D: Dimension,
+{
+    pub(crate) fn maybe_uninit<Sh>(shape: Sh) -> Self
+    where
+        Sh: ShapeBuilder<Dim = D>,
+    {
+        unsafe {
+            let shape = shape.into_shape();
+            let size = size_of_shape_checked_unwrap!(&shape.dim);
+            let mut v = Vec::with_capacity(size);
+            v.set_len(size);
+            Self::from_shape_vec_unchecked(shape, v)
+        }
+    }
+}

src/impl_owned_array.rs

@@ -1,4 +1,8 @@
+use std::mem::MaybeUninit;
+use std::mem::transmute;
+
 use crate::imp_prelude::*;
+use crate::OwnedRepr;
 
 /// Methods specific to `Array0`.
 ///
@@ -57,3 +61,33 @@ where
         self.data.0
     }
 }
+
+/// Methods specific to `Array` of `MaybeUninit`.
+///
+/// ***See also all methods for [`ArrayBase`]***
+///
+/// [`ArrayBase`]: struct.ArrayBase.html
+impl<A, D> Array<MaybeUninit<A>, D>
+where
+    D: Dimension,
+{
+    /// Assert that the array's storage's elements are all fully initialized, and conver
+    /// the array from element type `MaybeUninit<A>` to `A`.
+    pub(crate) unsafe fn assume_init(self) -> Array<A, D> {
+        // NOTE: Fully initialized includes elements not reachable in current slicing/view.
+        //
+        // Should this method be generalized to all array types?
+        // (Will need a way to map the RawData<Elem=X> to RawData<Elem=Y> of same kind)
+        let data = transmute::<OwnedRepr<MaybeUninit<A>>, OwnedRepr<A>>(self.data);
+        let ptr = self.ptr.cast::<A>();
+        let dim = self.dim;
+        let strides = self.strides;
+
+        Array {
+            data,
+            ptr,
+            dim,
+            strides,
+        }
+    }
+}