use std::rc::Rc;
use std::cell::RefCell;

#[derive(Debug)]
struct GroundStation {
  radio_freq: f64 // Mhz
}

fn main() {
  let base: Rc<RefCell<GroundStation>> = Rc::new(RefCell::new(
    GroundStation {
      radio_freq: 87.65
    }
  ));

  println!("base: {:?}", base);

  { // introduce a new scope
    let mut base_2 = base.borrow_mut();
    base_2.radio_freq -= 12.34;
    println!("base_2: {:?}", base_2);
  }

  println!("base: {:?}", base);

  let mut base_3 = base.borrow_mut();
  base_3.radio_freq += 43.21;

  println!("base: {:?}", base);
  println!("base_3: {:?}", base_3);
}