make Allocator object-safe

add test to ensure object-safety
This allows for runtime polymorphic allocators

1 files changed, 4 insertions, 1 deletions

diff --git a/library/core/src/alloc/mod.rs b/library/core/src/alloc/mod.rs
index 045eb58d013..9c2a0146e2c 100644
--- a/library/core/src/alloc/mod.rs
+++ b/library/core/src/alloc/mod.rs
@@ -342,7 +342,10 @@ pub unsafe trait Allocator {
     ///
     /// The returned adaptor also implements `Allocator` and will simply borrow this.
     #[inline(always)]
-    fn by_ref(&self) -> &Self {
+    fn by_ref(&self) -> &Self
+    where
+        Self: Sized,
+    {
         self
     }
 }