#![allow(dead_code, deprecated, unused_variables, unused_mut)]
use std::cell::{RefCell, Ref};
fn main() {
    let c = RefCell::new((5, 'b'));
    let b1: Ref<'_, (u32, char)> = c.borrow();
    let b2: Ref<'_, u32> = Ref::map(b1, |t| &t.0);
    assert_eq!(* b2, 5)
}