From 179f63dafcf9463b48d82e8698a844e18bf94370 Mon Sep 17 00:00:00 2001
From: Bastian Kauschke <bastian_kauschke@hotmail.de>
Date: Tue, 22 Sep 2020 21:35:43 +0200
Subject: [PATCH] add array from_ref

---
 library/core/src/array/mod.rs | 14 ++++++++++++++
 library/core/tests/array.rs   | 17 ++++++++++++++++-
 library/core/tests/lib.rs     |  1 +
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/library/core/src/array/mod.rs b/library/core/src/array/mod.rs
index c1d3aca6fdd..5730074bf27 100644
--- a/library/core/src/array/mod.rs
+++ b/library/core/src/array/mod.rs
@@ -19,6 +19,20 @@ mod iter;
 #[unstable(feature = "array_value_iter", issue = "65798")]
 pub use iter::IntoIter;
 
+/// Converts a reference to `T` into a reference to an array of length 1 (without copying).
+#[unstable(feature = "array_from_ref", issue = "none")]
+pub fn from_ref<T>(s: &T) -> &[T; 1] {
+    // SAFETY: Converting `&T` to `&[T; 1]` is sound.
+    unsafe { &*(s as *const T).cast::<[T; 1]>() }
+}
+
+/// Converts a mutable reference to `T` into a mutable reference to an array of length 1 (without copying).
+#[unstable(feature = "array_from_ref", issue = "none")]
+pub fn from_mut<T>(s: &mut T) -> &mut [T; 1] {
+    // SAFETY: Converting `&mut T` to `&mut [T; 1]` is sound.
+    unsafe { &mut *(s as *mut T).cast::<[T; 1]>() }
+}
+
 /// Utility trait implemented only on arrays of fixed size
 ///
 /// This trait can be used to implement other traits on fixed-size arrays
diff --git a/library/core/tests/array.rs b/library/core/tests/array.rs
index 5aba1a5d958..dbcea2747a0 100644
--- a/library/core/tests/array.rs
+++ b/library/core/tests/array.rs
@@ -1,4 +1,4 @@
-use core::array::{FixedSizeArray, IntoIter};
+use core::array::{self, FixedSizeArray, IntoIter};
 use core::convert::TryFrom;
 
 #[test]
@@ -19,6 +19,21 @@ fn fixed_size_array() {
     assert_eq!(FixedSizeArray::as_mut_slice(&mut empty_zero_sized).len(), 0);
 }
 
+#[test]
+fn array_from_ref() {
+    let value: String = "Hello World!".into();
+    let arr: &[String; 1] = array::from_ref(&value);
+    assert_eq!(&[value.clone()], arr);
+}
+
+#[test]
+fn array_from_mut() {
+    let mut value: String = "Hello World".into();
+    let arr: &mut [String; 1] = array::from_mut(&mut value);
+    arr[0].push_str("!");
+    assert_eq!(&value, "Hello World!");
+}
+
 #[test]
 fn array_try_from() {
     macro_rules! test {
diff --git a/library/core/tests/lib.rs b/library/core/tests/lib.rs
index 7e75c7cf47b..d8b36beb3e0 100644
--- a/library/core/tests/lib.rs
+++ b/library/core/tests/lib.rs
@@ -1,5 +1,6 @@
 #![feature(alloc_layout_extra)]
 #![feature(array_chunks)]
+#![feature(array_from_ref)]
 #![feature(array_methods)]
 #![feature(array_map)]
 #![feature(array_windows)]