Docs: impls of PartialEq/PartialOrd/Ord must agree

1 files changed, 4 insertions, 1 deletions

diff --git a/src/libcollections/binary_heap.rs b/src/libcollections/binary_heap.rs
index a5a2f70492d..0094804631b 100644
--- a/src/libcollections/binary_heap.rs
+++ b/src/libcollections/binary_heap.rs
@@ -42,8 +42,11 @@
 //! // instead of a max-heap.
 //! impl Ord for State {
 //!     fn cmp(&self, other: &State) -> Ordering {
-//!         // Notice that the we flip the ordering here
+//!         // Notice that the we flip the ordering on costs.
+//!         // In case of a tie we compare positions - this step is necessary
+//!         // to make implementations of `PartialEq` and `Ord` consistent.
 //!         other.cost.cmp(&self.cost)
+//!             .then_with(|| self.position.cmp(&other.position))
 //!     }
 //! }
 //!