pointer.rs

fn main() {
let mut val1 = 2;
val1 = 3; // OK

let val2 = 2;
//val2 = 3; // error: re-assignment of immutable variable
let  val1 = &mut 2;
*val1 = 3; // OK
    println!("Hello, world!");
    let box1=Box::new(3);
    let b=modify_foo(box1);
    println!("{}",b);
    let mut  r=3;
    let b2=modify_foo2(&mut r);
    println!("{}",b2);
    let mut b2=Box::new(5);
    *b2=6;
    
    let mut s = String::from("hello");

    change(&mut s);
    println!("{}",s);
}


fn change(some_string: &mut String) {

    some_string.push_str(", world");
}
fn modify_foo(mut foo: Box<i32>)->i32 { *foo += 1; *foo }
fn modify_foo2(foo: &mut i32)->i32 { *foo += 1; *foo }