Code shared from the Rust Playground

playground.rs

#![feature(nll)]

use std::cell::Cell;

trait Thing: Sized {
fn do_the_thing(&mut self, s: i32) {}
}

impl<T> Thing for Cell<T> {}

fn main() {
use std::ops::AddAssign;
let mut x = Cell::new(1);
let l = &x;
x                   // (1)
.do_the_thing(
        {
        x.set(3);
        l.set(4);
        x.get()  // (2)
    +
        l.get() // (4)
        }
    )     // (3)
;
}