Auto merge of #26008 - Marwes:arc_rc_as_ref, r=alexcrichton

The implementations are straightforward, I only hope I got the stability attributes correct(?).

src/liballoc/arc.rs

@@ -332,6 +332,15 @@ impl<T: ?Sized> Deref for Arc<T> {
     }
 }
 
+#[stable(feature = "rc_arc_as_ref", since = "1.2.0")]
+impl<T: ?Sized> AsRef<T> for Arc<T> {
+
+    #[inline]
+    fn as_ref(&self) -> &T {
+        &self.inner().data
+    }
+}
+
 impl<T: Clone> Arc<T> {
     /// Make a mutable reference from the given `Arc<T>`.
     ///

src/liballoc/rc.rs

@@ -156,6 +156,7 @@ use std::boxed;
 use core::cell::Cell;
 use core::clone::Clone;
 use core::cmp::{PartialEq, PartialOrd, Eq, Ord, Ordering};
+use core::convert::AsRef;
 use core::default::Default;
 use core::fmt;
 use core::hash::{Hasher, Hash};
@@ -379,6 +380,15 @@ impl<T: ?Sized> Deref for Rc<T> {
     }
 }
 
+#[stable(feature = "rc_arc_as_ref", since = "1.2.0")]
+impl<T: ?Sized> AsRef<T> for Rc<T> {
+
+    #[inline(always)]
+    fn as_ref(&self) -> &T {
+        &self.inner().value
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized> Drop for Rc<T> {
     /// Drops the `Rc<T>`.