cmp: Use default methods in trait Ord, only require Ord::lt

src/libstd/cmp.rs

@@ -157,19 +157,20 @@ pub fn lexical_ordering(o1: Ordering, o2: Ordering) -> Ordering {
 /**
 * Trait for values that can be compared for a sort-order.
 *
-* Eventually this may be simplified to only require
-* an `le` method, with the others generated from
-* default implementations. However it should remain
-* possible to implement the others separately, for
-* compatibility with floating-point NaN semantics
+* Ord only requires implementation of the `lt` method,
+* with the others generated from default implementations.
+*
+* However it remains possible to implement the others separately,
+* for compatibility with floating-point NaN semantics
 * (cf. IEEE 754-2008 section 5.11).
 */
+#[allow(default_methods)] // NOTE: Remove when allowed in stage0
 #[lang="ord"]
 pub trait Ord {
     fn lt(&self, other: &Self) -> bool;
-    fn le(&self, other: &Self) -> bool;
-    fn ge(&self, other: &Self) -> bool;
-    fn gt(&self, other: &Self) -> bool;
+    fn le(&self, other: &Self) -> bool { !other.lt(self) }
+    fn gt(&self, other: &Self) -> bool {  other.lt(self) }
+    fn ge(&self, other: &Self) -> bool { !self.lt(other) }
 }
 
 /// The equivalence relation. Two values may be equivalent even if they are

src/test/compile-fail/issue-3344.rs

@@ -9,8 +9,7 @@
 // except according to those terms.
 
 struct thing(uint);
-impl Ord for thing { //~ ERROR missing method `gt`
-    fn lt(&self, other: &thing) -> bool { **self < **other }
+impl Ord for thing { //~ ERROR missing method `lt`
     fn le(&self, other: &thing) -> bool { **self < **other }
     fn ge(&self, other: &thing) -> bool { **self < **other }
 }

src/test/run-pass/cmp-default.rs

@@ -0,0 +1,43 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Test default methods in Ord
+//
+struct Int(int);
+
+impl Ord for Int {
+    fn lt(&self, other: &Int) -> bool {
+        **self < **other
+    }
+}
+
+struct RevInt(int);
+
+impl Ord for RevInt {
+    fn lt(&self, other: &RevInt) -> bool {
+        **self > **other
+    }
+}
+
+pub fn main() {
+    assert!(Int(2) >  Int(1));
+    assert!(Int(2) >= Int(1));
+    assert!(Int(1) >= Int(1));
+    assert!(Int(1) <  Int(2));
+    assert!(Int(1) <= Int(2));
+    assert!(Int(1) <= Int(1));
+
+    assert!(RevInt(2) <  RevInt(1));
+    assert!(RevInt(2) <= RevInt(1));
+    assert!(RevInt(1) <= RevInt(1));
+    assert!(RevInt(1) >  RevInt(2));
+    assert!(RevInt(1) >= RevInt(2));
+    assert!(RevInt(1) >= RevInt(1));
+}