fn main() {
    // Storing an integer on the heap using Box
    let b = Box::new(5);
    println!("b = {}", b);

    // Box ensures single ownership of the heap-allocated data.
    // When 'b' goes out of scope, the memory for '5' on the heap is safely deallocated.

    // Example with a recursive data structure to illustrate Box's use in sizing.
    // Enums with recursive variants need Box to tell the compiler the size.
    enum List {
        Cons(i32, Box<List>),
        Nil,
    }

    use List::{Cons, Nil};

    let list = Cons(1, Box::new(Cons(2, Box::new(Cons(3, Box::new(Nil))))));
    // When 'list' goes out of scope, all allocated `Box`es are safely dropped.
}