libcore: add first_ref and second_ref to tuples

Author: erickt

src/libcore/core.rs

@@ -11,7 +11,7 @@ pub use GenericPath = path::GenericPath;
 pub use WindowsPath = path::WindowsPath;
 pub use PosixPath = path::PosixPath;
 
-pub use tuple::{TupleOps, ExtendedTupleOps};
+pub use tuple::{CopyableTuple, ImmutableTuple, ExtendedTupleOps};
 pub use str::{StrSlice, UniqueStr};
 pub use vec::{ConstVector, CopyableVector, ImmutableVector};
 pub use vec::{ImmutableEqVector, ImmutableCopyableVector};

src/libcore/tuple.rs

@@ -6,13 +6,13 @@
 
 use cmp::{Eq, Ord};
 
-pub trait TupleOps<T,U> {
+pub trait CopyableTuple<T, U> {
     pure fn first() -> T;
     pure fn second() -> U;
     pure fn swap() -> (U, T);
 }
 
-impl<T: Copy, U: Copy> (T, U): TupleOps<T,U> {
+impl<T: Copy, U: Copy> (T, U): CopyableTuple<T, U> {
 
     /// Return the first element of self
     pure fn first() -> T {
@@ -34,6 +34,24 @@ impl<T: Copy, U: Copy> (T, U): TupleOps<T,U> {
 
 }
 
+pub trait ImmutableTuple<T, U> {
+    pure fn first_ref(&self) -> &self/T;
+    pure fn second_ref(&self) -> &self/U;
+}
+
+impl<T, U> (T, U): ImmutableTuple<T, U> {
+    pure fn first_ref(&self) -> &self/T {
+        match *self {
+            (ref t, _) => t,
+        }
+    }
+    pure fn second_ref(&self) -> &self/U {
+        match *self {
+            (_, ref u) => u,
+        }
+    }
+}
+
 pub trait ExtendedTupleOps<A,B> {
     fn zip(&self) -> ~[(A, B)];
     fn map<C>(&self, f: &fn(a: &A, b: &B) -> C) -> ~[C];
@@ -145,6 +163,13 @@ impl<A: Ord, B: Ord, C: Ord> (A, B, C) : Ord {
     pure fn gt(other: &(A, B, C)) -> bool { (*other).lt(&self)  }
 }
 
+#[test]
+fn test_tuple_ref() {
+    let (~"foo", ~"bar");
+    assert x.first_ref() == &~"foo";
+    assert x.second_ref() == &~"bar";
+}
+
 #[test]
 #[allow(non_implicitly_copyable_typarams)]
 fn test_tuple() {