Specialize PartialOrd<A> for [A] where A: Ord

src/libcore/slice.rs

@@ -2290,6 +2290,28 @@ impl<A> SlicePartialOrd<A> for [A]
  }
 }
 
+impl<A> SlicePartialOrd<A> for [A]
+ where A: Ord
+{
+ default fn partial_compare(&self, other: &[A]) -> Option<Ordering> {
+ let l = cmp::min(self.len(), other.len());
+
+ // Slice to the loop iteration range to enable bound check
+ // elimination in the compiler
+ let lhs = &self[..l];
+ let rhs = &other[..l];
+
+ for i in 0..l {
+ match lhs[i].cmp(&rhs[i]) {
+ Ordering::Equal => (),
+ non_eq => return Some(non_eq),
+ }
+ }
+
+ self.len().partial_cmp(&other.len())
+ }
+}
+
 impl SlicePartialOrd<u8> for [u8] {
  #[inline]
  fn partial_compare(&self, other: &[u8]) -> Option<Ordering> {