use std::cell::{Cell, RefCell};
use std::rc::Rc;
use std::sync::Arc;

fn rc_cell() -> Rc<Cell<i32>> {
    let r = Rc::new(Cell::new(42));
    let x = r.get();
    r.set(x + x);
    r
}

fn rc_refcell() -> i32 {
    let r = Rc::new(RefCell::new(42));
    *r.borrow_mut() += 10;
    let x = *r.borrow();
    x
}

fn arc() -> Arc<i32> {
    let a = Arc::new(42);
    a
}

fn true_assert() {
    assert_eq!(1, 1);
}

fn main() {
    assert_eq!(*arc(), 42);
    assert_eq!(rc_cell().get(), 84);
    assert_eq!(rc_refcell(), 52);
    true_assert();
}

use std::cell::Cell;
use std::rc::Rc;
use std::sync::Arc;

fn rc_cell() -> Rc<Cell<i32>> {
    let r = Rc::new(Cell::new(42));
    let x = r.get();
    r.set(x + x);
    r
}

// TODO(solson): also requires destructors to run for the second borrow to work
// TODO(solson): needs StructWrappedNullablePointer support
// fn rc_refcell() -> i32 {
//     let r = Rc::new(RefCell::new(42));
//     *r.borrow_mut() += 10;
//     let x = *r.borrow();
//     x
// }

fn arc() -> Arc<i32> {
    let a = Arc::new(42);
    a
}

fn true_assert() {
    assert_eq!(1, 1);
}

fn main() {
    assert_eq!(*arc(), 42);
    assert_eq!(rc_cell().get(), 84);
    true_assert();
}

--- 
+++ 
@@ -1,4 +1,4 @@
-use std::cell::Cell;
+use std::cell::{Cell, RefCell};
 use std::rc::Rc;
 use std::sync::Arc;
 
@@ -9,14 +9,12 @@
     r
 }
 
-// TODO(solson): also requires destructors to run for the second borrow to work
-// TODO(solson): needs StructWrappedNullablePointer support
-// fn rc_refcell() -> i32 {
-//     let r = Rc::new(RefCell::new(42));
-//     *r.borrow_mut() += 10;
-//     let x = *r.borrow();
-//     x
-// }
+fn rc_refcell() -> i32 {
+    let r = Rc::new(RefCell::new(42));
+    *r.borrow_mut() += 10;
+    let x = *r.borrow();
+    x
+}
 
 fn arc() -> Arc<i32> {
     let a = Arc::new(42);
@@ -30,5 +28,6 @@
 fn main() {
     assert_eq!(*arc(), 42);
     assert_eq!(rc_cell().get(), 84);
+    assert_eq!(rc_refcell(), 52);
     true_assert();
 }
Enable an old test that works now!
