From 9adb45946dc9aa6a0f7203003330820d1f521887 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Gabriel=20Bj=C3=B8rnager=20Jensen?= <gabriel@achernar.io>
Date: Mon, 16 Dec 2024 10:42:26 +0100
Subject: [PATCH] Add 'into_array' conversion destructors for 'Box', 'Rc', and
 'Arc';

---
 alloc/src/boxed.rs | 20 ++++++++++++++++++++
 alloc/src/rc.rs    | 20 ++++++++++++++++++++
 alloc/src/sync.rs  | 20 ++++++++++++++++++++
 3 files changed, 60 insertions(+)

diff --git a/alloc/src/boxed.rs b/alloc/src/boxed.rs
index 23b85fbd4ebc3..ca3bd24a42031 100644
--- a/alloc/src/boxed.rs
+++ b/alloc/src/boxed.rs
@@ -761,6 +761,26 @@ impl<T> Box<[T]> {
         };
         unsafe { Ok(RawVec::from_raw_parts_in(ptr.as_ptr(), len, Global).into_box(len)) }
     }
+
+    /// Converts the boxed slice into a boxed array.
+    ///
+    /// This operation does not reallocate; the underlying array of the slice is simply reinterpreted as an array type.
+    ///
+    /// If `N` is not exactly equal to the length of `self`, then this method returns `None`.
+    #[unstable(feature = "slice_as_array", issue = "133508")]
+    #[inline]
+    #[must_use]
+    pub fn into_array<const N: usize>(self) -> Option<Box<[T; N]>> {
+        if self.len() == N {
+            let ptr = Self::into_raw(self) as *mut [T; N];
+
+            // SAFETY: The underlying array of a slice has the exact same layout as an actual array `[T; N]` if `N` is equal to the slice's length.
+            let me = unsafe { Box::from_raw(ptr) };
+            Some(me)
+        } else {
+            None
+        }
+    }
 }
 
 impl<T, A: Allocator> Box<[T], A> {
diff --git a/alloc/src/rc.rs b/alloc/src/rc.rs
index b7ec3af9818a0..e014404eff35b 100644
--- a/alloc/src/rc.rs
+++ b/alloc/src/rc.rs
@@ -1084,6 +1084,26 @@ impl<T> Rc<[T]> {
             ))
         }
     }
+
+    /// Converts the reference-counted slice into a reference-counted array.
+    ///
+    /// This operation does not reallocate; the underlying array of the slice is simply reinterpreted as an array type.
+    ///
+    /// If `N` is not exactly equal to the length of `self`, then this method returns `None`.
+    #[unstable(feature = "slice_as_array", issue = "133508")]
+    #[inline]
+    #[must_use]
+    pub fn into_array<const N: usize>(self) -> Option<Rc<[T; N]>> {
+        if self.len() == N {
+            let ptr = Self::into_raw(self) as *const [T; N];
+
+            // SAFETY: The underlying array of a slice has the exact same layout as an actual array `[T; N]` if `N` is equal to the slice's length.
+            let me = unsafe { Rc::from_raw(ptr) };
+            Some(me)
+        } else {
+            None
+        }
+    }
 }
 
 impl<T, A: Allocator> Rc<[T], A> {
diff --git a/alloc/src/sync.rs b/alloc/src/sync.rs
index 9be0b3e3e8801..b34a6d3f660c8 100644
--- a/alloc/src/sync.rs
+++ b/alloc/src/sync.rs
@@ -1203,6 +1203,26 @@ impl<T> Arc<[T]> {
             ))
         }
     }
+
+    /// Converts the reference-counted slice into a reference-counted array.
+    ///
+    /// This operation does not reallocate; the underlying array of the slice is simply reinterpreted as an array type.
+    ///
+    /// If `N` is not exactly equal to the length of `self`, then this method returns `None`.
+    #[unstable(feature = "slice_as_array", issue = "133508")]
+    #[inline]
+    #[must_use]
+    pub fn into_array<const N: usize>(self) -> Option<Arc<[T; N]>> {
+        if self.len() == N {
+            let ptr = Self::into_raw(self) as *const [T; N];
+
+            // SAFETY: The underlying array of a slice has the exact same layout as an actual array `[T; N]` if `N` is equal to the slice's length.
+            let me = unsafe { Arc::from_raw(ptr) };
+            Some(me)
+        } else {
+            None
+        }
+    }
 }
 
 impl<T, A: Allocator> Arc<[T], A> {