add a TotalEq trait

1 files changed, 44 insertions, 11 deletions

diff --git a/src/libcore/cmp.rs b/src/libcore/cmp.rs
index bc5b4b7f148..95f6f9bc1b5 100644
--- a/src/libcore/cmp.rs
+++ b/src/libcore/cmp.rs
@@ -1,4 +1,4 @@
-// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
@@ -21,15 +21,13 @@ and `Eq` to overload the `==` and `!=` operators.
 */
 
 /**
-* Trait for values that can be compared for equality
-* and inequality.
+* Trait for values that can be compared for equality and inequality.
 *
-* Eventually this may be simplified to only require
-* an `eq` method, with the other generated from
-* a default implementation. However it should
-* remain possible to implement `ne` separately, for
-* compatibility with floating-point NaN semantics
-* (cf. IEEE 754-2008 section 5.11).
+* This trait allows partial equality, where types can be unordered instead of strictly equal or
+* unequal. For example, with the built-in floating-point types `a == b` and `a != b` will both
+* evaluate to false if either `a` or `b` is NaN (cf. IEEE 754-2008 section 5.11).
+*
+* Eventually, this will be implemented by default for types that implement `TotalEq`.
 */
 #[lang="eq"]
 pub trait Eq {
@@ -37,11 +35,40 @@ pub trait Eq {
     fn ne(&self, other: &Self) -> bool;
 }
 
+/// Trait for equality comparisons where `a == b` and `a != b` are strict inverses.
+pub trait TotalEq {
+    fn equals(&self, other: &Self) -> bool;
+}
+
+macro_rules! totaleq_impl(
+    ($t:ty) => {
+        impl TotalEq for $t {
+            #[inline(always)]
+            fn equals(&self, other: &$t) -> bool { *self == *other }
+        }
+    }
+)
+
+totaleq_impl!(bool)
+
+totaleq_impl!(u8)
+totaleq_impl!(u16)
+totaleq_impl!(u32)
+totaleq_impl!(u64)
+
+totaleq_impl!(i8)
+totaleq_impl!(i16)
+totaleq_impl!(i32)
+totaleq_impl!(i64)
+
+totaleq_impl!(int)
+totaleq_impl!(uint)
+
 #[deriving(Eq)]
 pub enum Ordering { Less, Equal, Greater }
 
 /// Trait for types that form a total order
-pub trait TotalOrd {
+pub trait TotalOrd: TotalEq {
     fn cmp(&self, other: &Self) -> Ordering;
 }
 
@@ -140,11 +167,17 @@ pub fn max<T:Ord>(v1: T, v2: T) -> T {
 #[cfg(test)]
 mod test {
     #[test]
-    fn test_int() {
+    fn test_int_totalord() {
         assert_eq!(5.cmp(&10), Less);
         assert_eq!(10.cmp(&5), Greater);
         assert_eq!(5.cmp(&5), Equal);
         assert_eq!((-5).cmp(&12), Less);
         assert_eq!(12.cmp(-5), Greater);
     }
+
+    #[test]
+    fn test_int_totaleq() {
+        fail_unless!(5.equals(&5));
+        fail_unless!(!2.equals(&17));
+    }
 }