Overload the `==` operator

- String == &str == CowString
- Vec ==  &[T] ==  &mut [T] == [T, ..N] == CowVec
- InternedString == &str

5 files changed, 62 insertions, 16 deletions

diff --git a/src/libcore/array.rs b/src/libcore/array.rs
index 60765e82cb4..ffaf35414ea 100644
--- a/src/libcore/array.rs
+++ b/src/libcore/array.rs
@@ -18,6 +18,7 @@ use clone::Clone;
 use cmp::{PartialEq, Eq, PartialOrd, Ord, Ordering};
 use fmt;
 use kinds::Copy;
+use ops::Deref;
 use option::Option;
 
 // macro for implementing n-ary tuple functions and operations
@@ -39,17 +40,37 @@ macro_rules! array_impls {
             }
 
             #[unstable = "waiting for PartialEq to stabilize"]
-            impl<T:PartialEq> PartialEq for [T, ..$N] {
+            impl<A, B> PartialEq<[B, ..$N]> for [A, ..$N] where A: PartialEq<B> {
                 #[inline]
-                fn eq(&self, other: &[T, ..$N]) -> bool {
+                fn eq(&self, other: &[B, ..$N]) -> bool {
                     self[] == other[]
                 }
                 #[inline]
-                fn ne(&self, other: &[T, ..$N]) -> bool {
+                fn ne(&self, other: &[B, ..$N]) -> bool {
                     self[] != other[]
                 }
             }
 
+            impl<'a, A, B, Rhs> PartialEq<Rhs> for [A, ..$N] where
+                A: PartialEq<B>,
+                Rhs: Deref<[B]>,
+            {
+                #[inline(always)]
+                fn eq(&self, other: &Rhs) -> bool { PartialEq::eq(self[], &**other) }
+                #[inline(always)]
+                fn ne(&self, other: &Rhs) -> bool { PartialEq::ne(self[], &**other) }
+            }
+
+            impl<'a, A, B, Lhs> PartialEq<[B, ..$N]> for Lhs where
+                A: PartialEq<B>,
+                Lhs: Deref<[A]>
+            {
+                #[inline(always)]
+                fn eq(&self, other: &[B, ..$N]) -> bool { PartialEq::eq(&**self, other[]) }
+                #[inline(always)]
+                fn ne(&self, other: &[B, ..$N]) -> bool { PartialEq::ne(&**self, other[]) }
+            }
+
             #[unstable = "waiting for Eq to stabilize"]
             impl<T:Eq> Eq for [T, ..$N] { }
 
diff --git a/src/libcore/borrow.rs b/src/libcore/borrow.rs
index 06fda8d6092..b88fb914dd8 100644
--- a/src/libcore/borrow.rs
+++ b/src/libcore/borrow.rs
@@ -196,9 +196,12 @@ impl<'a, T, Sized? B> Ord for Cow<'a, T, B> where B: Ord + ToOwned<T> {
     }
 }
 
-impl<'a, T, Sized? B> PartialEq for Cow<'a, T, B> where B: PartialEq + ToOwned<T> {
+impl<'a, 'b, T, U, Sized? B, Sized? C> PartialEq<Cow<'b, U, C>> for Cow<'a, T, B> where
+    B: PartialEq<C> + ToOwned<T>,
+    C: ToOwned<U>,
+{
     #[inline]
-    fn eq(&self, other: &Cow<'a, T, B>) -> bool {
+    fn eq(&self, other: &Cow<'b, U, C>) -> bool {
         PartialEq::eq(&**self, &**other)
     }
 }
diff --git a/src/libcore/cmp.rs b/src/libcore/cmp.rs
index 11878dc76d9..d5001a08b1d 100644
--- a/src/libcore/cmp.rs
+++ b/src/libcore/cmp.rs
@@ -400,11 +400,11 @@ mod impls {
     // & pointers
 
     #[unstable = "Trait is unstable."]
-    impl<'a, Sized? T: PartialEq> PartialEq for &'a T {
+    impl<'a, 'b, Sized? A, Sized? B> PartialEq<&'b B> for &'a A where A: PartialEq<B> {
         #[inline]
-        fn eq(&self, other: & &'a T) -> bool { PartialEq::eq(*self, *other) }
+        fn eq(&self, other: & &'b B) -> bool { PartialEq::eq(*self, *other) }
         #[inline]
-        fn ne(&self, other: & &'a T) -> bool { PartialEq::ne(*self, *other) }
+        fn ne(&self, other: & &'b B) -> bool { PartialEq::ne(*self, *other) }
     }
     #[unstable = "Trait is unstable."]
     impl<'a, Sized? T: PartialOrd> PartialOrd for &'a T {
@@ -432,11 +432,11 @@ mod impls {
     // &mut pointers
 
     #[unstable = "Trait is unstable."]
-    impl<'a, Sized? T: PartialEq> PartialEq for &'a mut T {
+    impl<'a, 'b, Sized? A, Sized? B> PartialEq<&'b mut B> for &'a mut A where A: PartialEq<B> {
         #[inline]
-        fn eq(&self, other: &&'a mut T) -> bool { PartialEq::eq(*self, *other) }
+        fn eq(&self, other: &&'b mut B) -> bool { PartialEq::eq(*self, *other) }
         #[inline]
-        fn ne(&self, other: &&'a mut T) -> bool { PartialEq::ne(*self, *other) }
+        fn ne(&self, other: &&'b mut B) -> bool { PartialEq::ne(*self, *other) }
     }
     #[unstable = "Trait is unstable."]
     impl<'a, Sized? T: PartialOrd> PartialOrd for &'a mut T {
@@ -460,4 +460,18 @@ mod impls {
     }
     #[unstable = "Trait is unstable."]
     impl<'a, Sized? T: Eq> Eq for &'a mut T {}
+
+    impl<'a, 'b, Sized? A, Sized? B> PartialEq<&'b mut B> for &'a A where A: PartialEq<B> {
+        #[inline]
+        fn eq(&self, other: &&'b mut B) -> bool { PartialEq::eq(*self, *other) }
+        #[inline]
+        fn ne(&self, other: &&'b mut B) -> bool { PartialEq::ne(*self, *other) }
+    }
+
+    impl<'a, 'b, Sized? A, Sized? B> PartialEq<&'b B> for &'a mut A where A: PartialEq<B> {
+        #[inline]
+        fn eq(&self, other: &&'b B) -> bool { PartialEq::eq(*self, *other) }
+        #[inline]
+        fn ne(&self, other: &&'b B) -> bool { PartialEq::ne(*self, *other) }
+    }
 }
diff --git a/src/libcore/iter.rs b/src/libcore/iter.rs
index 2d488a4b155..f9595f0663d 100644
--- a/src/libcore/iter.rs
+++ b/src/libcore/iter.rs
@@ -2473,7 +2473,11 @@ pub mod order {
     }
 
     /// Compare `a` and `b` for equality (Using partial equality, `PartialEq`)
-    pub fn eq<A: PartialEq, T: Iterator<A>, S: Iterator<A>>(mut a: T, mut b: S) -> bool {
+    pub fn eq<A, B, L, R>(mut a: L, mut b: R) -> bool where
+        A: PartialEq<B>,
+        L: Iterator<A>,
+        R: Iterator<B>,
+    {
         loop {
             match (a.next(), b.next()) {
                 (None, None) => return true,
@@ -2484,7 +2488,11 @@ pub mod order {
     }
 
     /// Compare `a` and `b` for nonequality (Using partial equality, `PartialEq`)
-    pub fn ne<A: PartialEq, T: Iterator<A>, S: Iterator<A>>(mut a: T, mut b: S) -> bool {
+    pub fn ne<A, B, L, R>(mut a: L, mut b: R) -> bool where
+        A: PartialEq<B>,
+        L: Iterator<A>,
+        R: Iterator<B>,
+    {
         loop {
             match (a.next(), b.next()) {
                 (None, None) => return false,
diff --git a/src/libcore/slice.rs b/src/libcore/slice.rs
index 950f04a5d97..b445dba6117 100644
--- a/src/libcore/slice.rs
+++ b/src/libcore/slice.rs
@@ -1802,12 +1802,12 @@ pub mod bytes {
 //
 
 #[unstable = "waiting for DST"]
-impl<T: PartialEq> PartialEq for [T] {
-    fn eq(&self, other: &[T]) -> bool {
+impl<A, B> PartialEq<[B]> for [A] where A: PartialEq<B> {
+    fn eq(&self, other: &[B]) -> bool {
         self.len() == other.len() &&
             order::eq(self.iter(), other.iter())
     }
-    fn ne(&self, other: &[T]) -> bool {
+    fn ne(&self, other: &[B]) -> bool {
         self.len() != other.len() ||
             order::ne(self.iter(), other.iter())
     }