Implement RFC#28: Add PartialOrd::partial_cmp

I ended up altering the semantics of Json's PartialOrd implementation.
It used to be the case that Null < Null, but I can't think of any reason
for an ordering other than the default one so I just switched it over to
using the derived implementation.

This also fixes broken `PartialOrd` implementations for `Vec` and
`TreeMap`.

RFC: 0028-partial-cmp

2 files changed, 6 insertions, 5 deletions

diff --git a/src/libnum/bigint.rs b/src/libnum/bigint.rs
index 9011aafc009..cc3753def59 100644
--- a/src/libnum/bigint.rs
+++ b/src/libnum/bigint.rs
@@ -91,8 +91,8 @@ impl Eq for BigUint {}
 
 impl PartialOrd for BigUint {
     #[inline]
-    fn lt(&self, other: &BigUint) -> bool {
-        self.cmp(other) == Less
+    fn partial_cmp(&self, other: &BigUint) -> Option<Ordering> {
+        Some(self.cmp(other))
     }
 }
 
@@ -816,8 +816,8 @@ impl Eq for BigInt {}
 
 impl PartialOrd for BigInt {
     #[inline]
-    fn lt(&self, other: &BigInt) -> bool {
-        self.cmp(other) == Less
+    fn partial_cmp(&self, other: &BigInt) -> Option<Ordering> {
+        Some(self.cmp(other))
     }
 }
 
diff --git a/src/libnum/rational.rs b/src/libnum/rational.rs
index 971b6b1b51b..9a455edf2c0 100644
--- a/src/libnum/rational.rs
+++ b/src/libnum/rational.rs
@@ -193,7 +193,8 @@ macro_rules! cmp_impl {
     };
 }
 cmp_impl!(impl PartialEq, eq, ne)
-cmp_impl!(impl PartialOrd, lt, gt, le, ge)
+cmp_impl!(impl PartialOrd, lt -> bool, gt -> bool, le -> bool, ge -> bool,
+          partial_cmp -> Option<cmp::Ordering>)
 cmp_impl!(impl Eq, )
 cmp_impl!(impl Ord, cmp -> cmp::Ordering)