fn wtf(vector: &mut Vec<i32>) { // mutable borrow starts here
    vector.push(20)
} // mutable borrow also ends here


fn main() {
    let mut p: Vec<i32> = vec![1, 2, 3];
    {
        let x = &mut p; // lifetime of mutable borrow starts here
        x.push(42);
    } // life-time of x ends here

    wtf(&mut p);

    println!("{:?}", p); // & to P...we have one mutable ref, one immutable ref
    //-- why no compile time error???
}