librustc (RFC rust-lang#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 rust-lang#6515.

[breaking-change]

Author: pcwalton

src/etc/vim/syntax/rust.vim

@@ -65,7 +65,7 @@ syn keyword   rustTrait       Copy Send Sized Share
 syn keyword   rustTrait       Add Sub Mul Div Rem Neg Not
 syn keyword   rustTrait       BitAnd BitOr BitXor
 syn keyword   rustTrait       Drop Deref DerefMut
-syn keyword   rustTrait       Shl Shr Index
+syn keyword   rustTrait       Shl Shr Index IndexMut
 syn keyword   rustEnum        Option
 syn keyword   rustEnumVariant Some None
 syn keyword   rustEnum        Result

src/libcollections/bitv.rs

@@ -16,14 +16,36 @@ use core::cmp;
 use core::default::Default;
 use core::fmt;
 use core::iter::Take;
-use core::ops;
 use core::slice;
 use core::uint;
 use std::hash;
 
 use {Collection, Mutable, Set, MutableSet};
 use vec::Vec;
 
+#[cfg(not(stage0))]
+use core::ops::Index;
+
+#[cfg(not(stage0))]
+static TRUE: bool = true;
+
+#[cfg(not(stage0))]
+static FALSE: bool = false;
+
+#[deriving(Clone)]
+struct SmallBitv {
+    /// only the lowest nbits of this value are used. the rest is undefined.
+    bits: uint
+}
+
+#[deriving(Clone)]
+struct BigBitv {
+    storage: Vec<uint>
+}
+
+#[deriving(Clone)]
+enum BitvVariant { Big(BigBitv), Small(SmallBitv) }
+
 /// The bitvector type
 ///
 /// # Example
@@ -58,6 +80,18 @@ pub struct Bitv {
     nbits: uint
 }
 
+#[cfg(not(stage0))]
+impl Index<uint,bool> for Bitv {
+    #[inline]
+    fn index<'a>(&'a self, i: &uint) -> &'a bool {
+        if self.get(*i) {
+            &TRUE
+        } else {
+            &FALSE
+        }
+    }
+}
+
 struct MaskWords<'a> {
     iter: slice::Items<'a, uint>,
     next_word: Option<&'a uint>,
@@ -268,7 +302,7 @@ impl Bitv {
             if offset >= bitv.nbits {
                 0
             } else {
-                bitv[offset] as u8 << (7 - bit)
+                bitv.get(offset) as u8 << (7 - bit)
             }
         }
 
@@ -286,6 +320,13 @@ impl Bitv {
         )
     }
 
+    /**
+     * Transform `self` into a `Vec<bool>` by turning each bit into a `bool`.
+     */
+    pub fn to_bools(&self) -> Vec<bool> {
+        Vec::from_fn(self.nbits, |i| self.get(i))
+    }
+
     /**
      * Compare a bitvector to a vector of `bool`.
      *
@@ -504,13 +545,6 @@ impl Clone for Bitv {
     }
 }
 
-impl ops::Index<uint,bool> for Bitv {
-    #[inline]
-    fn index(&self, i: &uint) -> bool {
-        self.get(*i)
-    }
-}
-
 impl fmt::Show for Bitv {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
         for bit in self.iter() {
@@ -1369,9 +1403,9 @@ mod tests {
         b2.set(1, true);
         b2.set(2, true);
         assert!(b1.difference(&b2));
-        assert!(b1[0]);
-        assert!(!b1[1]);
-        assert!(!b1[2]);
+        assert!(b1.get(0));
+        assert!(!b1.get(1));
+        assert!(!b1.get(2));
     }
 
     #[test]
@@ -1383,9 +1417,9 @@ mod tests {
         b2.set(40, true);
         b2.set(80, true);
         assert!(b1.difference(&b2));
-        assert!(b1[0]);
-        assert!(!b1[40]);
-        assert!(!b1[80]);
+        assert!(b1.get(0));
+        assert!(!b1.get(40));
+        assert!(!b1.get(80));
     }
 
     #[test]

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;
 }
 
 /**

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};
 

src/librustc/middle/lang_items.rs

@@ -234,6 +234,7 @@ lets_do_this! {
     ShlTraitLangItem,                "shl",                     shl_trait;
     ShrTraitLangItem,                "shr",                     shr_trait;
     IndexTraitLangItem,              "index",                   index_trait;
+    IndexMutTraitLangItem,           "index_mut",               index_mut_trait;
 
     UnsafeTypeLangItem,              "unsafe",                  unsafe_type;
 

src/librustc/middle/mem_categorization.rs

@@ -443,10 +443,6 @@ impl<'t,TYPER:Typer> MemCategorizationContext<'t,TYPER> {
           }
 
           ast::ExprIndex(ref base, _) => {
-            if self.typer.is_method_call(expr.id) {
-                return Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty));
-            }
-
             let base_cmt = if_ok!(self.cat_expr(&**base));
             Ok(self.cat_index(expr, base_cmt, 0))
           }
@@ -759,7 +755,7 @@ impl<'t,TYPER:Typer> MemCategorizationContext<'t,TYPER> {
 
     pub fn cat_index<N:ast_node>(&self,
                                  elt: &N,
-                                 base_cmt: cmt,
+                                 mut base_cmt: cmt,
                                  derefs: uint)
                                  -> cmt {
         //! Creates a cmt for an indexing operation (`[]`); this
@@ -793,14 +789,26 @@ impl<'t,TYPER:Typer> MemCategorizationContext<'t,TYPER> {
         //! - `derefs`: the deref number to be used for
         //!   the implicit index deref, if any (see above)
 
-        let element_ty = match ty::array_element_ty(base_cmt.ty) {
-          Some(ref mt) => mt.ty,
-          None => {
-            self.tcx().sess.span_bug(
-                elt.span(),
-                format!("Explicit index of non-index type `{}`",
-                        base_cmt.ty.repr(self.tcx())).as_slice());
-          }
+        let method_call = typeck::MethodCall::expr(elt.id());
+        let method_ty = self.typer.node_method_ty(method_call);
+
+        let element_ty = match method_ty {
+            Some(method_ty) => {
+                let ref_ty = ty::ty_fn_ret(method_ty);
+                base_cmt = self.cat_rvalue_node(elt.id(), elt.span(), ref_ty);
+                *ty::ty_fn_args(method_ty).get(0)
+            }
+            None => {
+                match ty::array_element_ty(base_cmt.ty) {
+                    Some(ref mt) => mt.ty,
+                    None => {
+                        self.tcx().sess.span_bug(
+                            elt.span(),
+                            format!("Explicit index of non-index type `{}`",
+                                    base_cmt.ty.repr(self.tcx())).as_slice());
+                    }
+                }
+            }
         };
 
         return match deref_kind(self.tcx(), base_cmt.ty) {