Macro define_with 

macro_rules! define_with {
    ($shared:expr) => { ... };
}

Convenience macro for invoking Shared::with() method.

let mut shared_data = Rc::new(RefCell::new(vec![1, 2, 3]));
define_with!(shared_data);

with!(|data| data.push(42));

let copy: Vec<_> = with!(|data| data.clone());

assert_eq!(copy, vec![1, 2, 3, 42]);