librustc (RFC #34): Implement the new `Index` and `IndexMut` traits.

This will break code that used the old `Index` trait. Change this code
to use the new `Index` traits. For reference, here are their signatures:

    pub trait Index<Index,Result> {
        fn index<'a>(&'a self, index: &Index) -> &'a Result;
    }
    pub trait IndexMut<Index,Result> {
        fn index_mut<'a>(&'a mut self, index: &Index) -> &'a mut Result;
    }

Closes #6515.

[breaking-change]

2 files changed, 40 insertions, 5 deletions

diff --git a/src/libcore/ops.rs b/src/libcore/ops.rs
index d42c09b8163..fc37fdde8f5 100644
--- a/src/libcore/ops.rs
+++ b/src/libcore/ops.rs
@@ -613,7 +613,7 @@ shr_impl!(uint u8 u16 u32 u64 int i8 i16 i32 i64)
 /**
  *
  * The `Index` trait is used to specify the functionality of indexing operations
- * like `arr[idx]`.
+ * like `arr[idx]` when used in an immutable context.
  *
  * # Example
  *
@@ -624,9 +624,9 @@ shr_impl!(uint u8 u16 u32 u64 int i8 i16 i32 i64)
  * struct Foo;
  *
  * impl Index<Foo, Foo> for Foo {
- *     fn index(&self, _rhs: &Foo) -> Foo {
+ *     fn index<'a>(&'a self, _rhs: &Foo) -> &'a Foo {
  *         println!("Indexing!");
- *         *self
+ *         self
  *     }
  * }
  *
@@ -636,9 +636,42 @@ shr_impl!(uint u8 u16 u32 u64 int i8 i16 i32 i64)
  * ```
  */
 #[lang="index"]
+#[cfg(not(stage0))]
 pub trait Index<Index,Result> {
     /// The method for the indexing (`Foo[Bar]`) operation
-    fn index(&self, index: &Index) -> Result;
+    fn index<'a>(&'a self, index: &Index) -> &'a Result;
+}
+
+/**
+ *
+ * The `IndexMut` trait is used to specify the functionality of indexing
+ * operations like `arr[idx]`, when used in a mutable context.
+ *
+ * # Example
+ *
+ * A trivial implementation of `IndexMut`. When `Foo[Foo]` happens, it ends up
+ * calling `index`, and therefore, `main` prints `Indexing!`.
+ *
+ * ```
+ * struct Foo;
+ *
+ * impl IndexMut<Foo, Foo> for Foo {
+ *     fn index_mut<'a>(&'a mut self, _rhs: &Foo) -> &'a mut Foo {
+ *         println!("Indexing!");
+ *         self
+ *     }
+ * }
+ *
+ * fn main() {
+ *     &mut Foo[Foo];
+ * }
+ * ```
+ */
+#[lang="index_mut"]
+#[cfg(not(stage0))]
+pub trait IndexMut<Index,Result> {
+    /// The method for the indexing (`Foo[Bar]`) operation
+    fn index_mut<'a>(&'a mut self, index: &Index) -> &'a mut Result;
 }
 
 /**
diff --git a/src/libcore/prelude.rs b/src/libcore/prelude.rs
index df9c0e67b0d..f967a2a5fa5 100644
--- a/src/libcore/prelude.rs
+++ b/src/libcore/prelude.rs
@@ -33,7 +33,9 @@ pub use kinds::{Copy, Send, Sized, Share};
 pub use ops::{Add, Sub, Mul, Div, Rem, Neg, Not};
 pub use ops::{BitAnd, BitOr, BitXor};
 pub use ops::{Drop, Deref, DerefMut};
-pub use ops::{Shl, Shr, Index};
+pub use ops::{Shl, Shr};
+#[cfg(not(stage0))]
+pub use ops::{Index, IndexMut};
 pub use option::{Option, Some, None};
 pub use result::{Result, Ok, Err};