From 7d040b7d13e6fb6e143f1c14987bcc2f48dc585b Mon Sep 17 00:00:00 2001
From: Avi Weinstock <aweinstock314@gmail.com>
Date: Tue, 19 Nov 2019 18:01:24 -0500
Subject: [PATCH] Add UninitScalar newtype for defining traits on a
 MaybeUninit<Scalar>.

---
 src/base/allocator.rs |  3 ++-
 src/base/scalar.rs    | 25 ++++++++++++++++++++++++-
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/src/base/allocator.rs b/src/base/allocator.rs
index 246f3620e..71db540ae 100644
--- a/src/base/allocator.rs
+++ b/src/base/allocator.rs
@@ -5,7 +5,7 @@ use std::any::Any;
 use crate::base::constraint::{SameNumberOfColumns, SameNumberOfRows, ShapeConstraint};
 use crate::base::dimension::{Dim, U1};
 use crate::base::storage::ContiguousStorageMut;
-use crate::base::{DefaultAllocator, Scalar};
+use crate::base::{DefaultAllocator, Scalar, UninitScalar};
 
 /// A matrix allocator of a memory buffer that may contain `R::to_usize() * C::to_usize()`
 /// elements of type `N`.
@@ -21,6 +21,7 @@ pub trait Allocator<N: Scalar + Copy, R: Dim, C: Dim = U1>: Any + Sized {
     type Buffer: ContiguousStorageMut<N, R, C> + Clone;
 
     /// Allocates a buffer with the given number of rows and columns without initializing its content.
+    //unsafe fn allocate_uninitialized(nrows: R, ncols: C) -> <Self as Allocator<UninitScalar<N>, R, C>>::Buffer;
     unsafe fn allocate_uninitialized(nrows: R, ncols: C) -> Self::Buffer;
 
     /// Allocates a buffer initialized with the content of the given iterator.
diff --git a/src/base/scalar.rs b/src/base/scalar.rs
index a6c837ffa..e9750825a 100644
--- a/src/base/scalar.rs
+++ b/src/base/scalar.rs
@@ -1,6 +1,7 @@
 use std::any::Any;
 use std::any::TypeId;
-use std::fmt::Debug;
+use std::fmt::{self, Debug, Formatter};
+use std::mem::MaybeUninit;
 
 /// The basic scalar type for all structures of `nalgebra`.
 ///
@@ -15,3 +16,25 @@ pub trait Scalar: PartialEq + Debug + Any {
     }
 }
 impl<T: Copy + PartialEq + Debug + Any> Scalar for T {}
+
+/// A newtype wrapper that provides the necessary trait implementations for MaybeUninit
+/// This is needed because MaybeUninit does not pass through implementations on uninitialized data (for good reason)
+pub struct UninitScalar<S: Scalar>(MaybeUninit<S>);
+
+impl<S: Scalar> Clone for UninitScalar<S> {
+    fn clone(&self) -> Self {
+        panic!("Clone::clone called on potentially uninitialized data")
+    }
+}
+
+impl<S: Scalar> PartialEq for UninitScalar<S> {
+    fn eq(&self, _: &Self) -> bool {
+        panic!("PartialEq::eq called on potentially uninitalized data")
+    }
+}
+impl<S: Scalar> Debug for UninitScalar<S> {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(f, "UninitScalar")
+    }
+}
+impl<S: Scalar> Scalar for UninitScalar<S> {}