RefCell vs normal refs

//https://play.rust-lang.org/?gist=c7fd2d14e8640ed21533ac27ecf1197e&version=stable

use std::cell::RefCell;

fn immutably_borrows(a: &i32) {
    println!("a is {}", a);
}
fn mutably_borrows(a: &mut i32) {
    *a +=1;
}

fn demo_1(mut r: &mut i32) {
    immutably_borrows(&r);
    mutably_borrows(&mut r);
    immutably_borrows(&r);
}

fn demo_2(r: &RefCell<i32>) {
    immutably_borrows(&r.borrow());
    mutably_borrows(&mut r.borrow_mut());
    immutably_borrows(&r.borrow());
}

fn main() {
    let mut data1 = 5;
    let data2 = RefCell::new(5);
    demo_1(&mut data1);
    demo_2(&data2);
}