std: Change RandomAccessIterator to use `&mut self`

Many iterators go through a closure when dealing with the `idx` method, which
are invalid after the previous change (closures cannot be invoked through a `&`
pointer). This commit alters the `fn idx` method on the RandomAccessIterator
to take `&mut self` rather than `&self`.

[breaking-change]

src/libcollections/bitv.rs

@@ -632,7 +632,7 @@ fn indexable(&self) -> uint {
     }
 
     #[inline]
-    fn idx(&self, index: uint) -> Option<bool> {
+    fn idx(&mut self, index: uint) -> Option<bool> {
         if index >= self.indexable() {
             None
         } else {

src/libcollections/ringbuf.rs

@@ -272,7 +272,7 @@ impl<'a, T> RandomAccessIterator<&'a T> for Items<'a, T> {
     fn indexable(&self) -> uint { self.rindex - self.index }
 
     #[inline]
-    fn idx(&self, j: uint) -> Option<&'a T> {
+    fn idx(&mut self, j: uint) -> Option<&'a T> {
         if j >= self.indexable() {
             None
         } else {

src/libstd/iter.rs

@@ -703,7 +703,7 @@ pub trait RandomAccessIterator<A>: Iterator<A> {
     fn indexable(&self) -> uint;
 
     /// Return an element at an index
-    fn idx(&self, index: uint) -> Option<A>;
+    fn idx(&mut self, index: uint) -> Option<A>;
 }
 
 /// An iterator that knows its exact length
@@ -771,8 +771,9 @@ impl<A, T: DoubleEndedIterator<A> + RandomAccessIterator<A>> RandomAccessIterato
     #[inline]
     fn indexable(&self) -> uint { self.iter.indexable() }
     #[inline]
-    fn idx(&self, index: uint) -> Option<A> {
-        self.iter.idx(self.indexable() - index - 1)
+    fn idx(&mut self, index: uint) -> Option<A> {
+        let amt = self.indexable();
+        self.iter.idx(amt - index - 1)
     }
 }
 
@@ -1071,7 +1072,7 @@ fn indexable(&self) -> uint {
     }
 
     #[inline]
-    fn idx(&self, index: uint) -> Option<A> {
+    fn idx(&mut self, index: uint) -> Option<A> {
         let liter = self.iter.indexable();
         let lorig = self.orig.indexable();
         if lorig == 0 {
@@ -1143,7 +1144,7 @@ fn indexable(&self) -> uint {
     }
 
     #[inline]
-    fn idx(&self, index: uint) -> Option<A> {
+    fn idx(&mut self, index: uint) -> Option<A> {
         let len = self.a.indexable();
         if index < len {
             self.a.idx(index)
@@ -1221,7 +1222,7 @@ fn indexable(&self) -> uint {
     }
 
     #[inline]
-    fn idx(&self, index: uint) -> Option<(A, B)> {
+    fn idx(&mut self, index: uint) -> Option<(A, B)> {
         match self.a.idx(index) {
             None => None,
             Some(x) => match self.b.idx(index) {
@@ -1276,8 +1277,9 @@ fn indexable(&self) -> uint {
     }
 
     #[inline]
-    fn idx(&self, index: uint) -> Option<B> {
-        self.do_map(self.iter.idx(index))
+    fn idx(&mut self, index: uint) -> Option<B> {
+        let elt = self.iter.idx(index);
+        self.do_map(elt)
     }
 }
 
@@ -1415,7 +1417,7 @@ fn indexable(&self) -> uint {
     }
 
     #[inline]
-    fn idx(&self, index: uint) -> Option<(uint, A)> {
+    fn idx(&mut self, index: uint) -> Option<(uint, A)> {
         match self.iter.idx(index) {
             Some(a) => Some((self.count + index, a)),
             _ => None,
@@ -1600,7 +1602,7 @@ fn indexable(&self) -> uint {
     }
 
     #[inline]
-    fn idx(&self, index: uint) -> Option<A> {
+    fn idx(&mut self, index: uint) -> Option<A> {
         if index >= self.indexable() {
             None
         } else {
@@ -1649,7 +1651,7 @@ fn indexable(&self) -> uint {
     }
 
     #[inline]
-    fn idx(&self, index: uint) -> Option<A> {
+    fn idx(&mut self, index: uint) -> Option<A> {
         if index >= self.n {
             None
         } else {
@@ -1799,7 +1801,7 @@ fn indexable(&self) -> uint {
     }
 
     #[inline]
-    fn idx(&self, index: uint) -> Option<A> {
+    fn idx(&mut self, index: uint) -> Option<A> {
         self.iter.idx(index)
     }
 }
@@ -1862,8 +1864,9 @@ fn indexable(&self) -> uint {
     }
 
     #[inline]
-    fn idx(&self, index: uint) -> Option<A> {
-        self.do_inspect(self.iter.idx(index))
+    fn idx(&mut self, index: uint) -> Option<A> {
+        let element = self.iter.idx(index);
+        self.do_inspect(element)
     }
 }
 
@@ -2164,7 +2167,7 @@ impl<A: Clone> RandomAccessIterator<A> for Repeat<A> {
     #[inline]
     fn indexable(&self) -> uint { uint::MAX }
     #[inline]
-    fn idx(&self, _: uint) -> Option<A> { Some(self.element.clone()) }
+    fn idx(&mut self, _: uint) -> Option<A> { Some(self.element.clone()) }
 }
 
 /// Functions for lexicographical ordering of sequences.

src/libstd/slice.rs

@@ -489,7 +489,7 @@ fn indexable(&self) -> uint {
     }
 
     #[inline]
-    fn idx(&self, index: uint) -> Option<&'a [T]> {
+    fn idx(&mut self, index: uint) -> Option<&'a [T]> {
         if index < self.indexable() {
             let lo = index * self.size;
             let mut hi = lo + self.size;
@@ -2095,7 +2095,7 @@ fn indexable(&self) -> uint {
     }
 
     #[inline]
-    fn idx(&self, index: uint) -> Option<&'a T> {
+    fn idx(&mut self, index: uint) -> Option<&'a T> {
         unsafe {
             if index < self.indexable() {
                 transmute(self.ptr.offset(index as int))