Add sync::Weak::ptr_eq

src/liballoc/sync.rs

@@ -1130,6 +1130,53 @@ fn inner(&self) -> Option<&ArcInner<T>> {
             Some(unsafe { self.ptr.as_ref() })
         }
     }
+
+    /// Returns true if the two `Weak`s point to the same value (not just values
+    /// that compare as equal).
+    ///
+    /// # Notes
+    ///
+    /// Since this compares pointers it means that `Weak::new()` will equal each
+    /// other, even though they don't point to any value.
+    ///
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(weak_ptr_eq)]
+    /// use std::sync::{Arc, Weak};
+    ///
+    /// let first_rc = Arc::new(5);
+    /// let first = Arc::downgrade(&first_rc);
+    /// let second = Arc::downgrade(&first_rc);
+    ///
+    /// assert!(Weak::ptr_eq(&first, &second));
+    ///
+    /// let third_rc = Arc::new(5);
+    /// let third = Arc::downgrade(&third_rc);
+    ///
+    /// assert!(!Weak::ptr_eq(&first, &third));
+    /// ```
+    ///
+    /// Comparing `Weak::new`.
+    ///
+    /// ```
+    /// #![feature(weak_ptr_eq)]
+    /// use std::sync::{Arc, Weak};
+    ///
+    /// let first = Weak::new();
+    /// let second = Weak::new();
+    /// assert!(Weak::ptr_eq(&first, &second));
+    ///
+    /// let third_rc = Arc::new(());
+    /// let third = Arc::downgrade(&third_rc);
+    /// assert!(!Weak::ptr_eq(&first, &third));
+    /// ```
+    #[inline]
+    #[unstable(feature = "weak_ptr_eq", issue = "55981")]
+    pub fn ptr_eq(this: &Self, other: &Self) -> bool {
+        this.ptr.as_ptr() == other.ptr.as_ptr()
+    }
 }
 
 #[stable(feature = "arc_weak", since = "1.4.0")]