Rust ownership and lifetimes

rust-ownership.rs

// This function takes ownership of the passed value
fn take_ownership(value: Box<i32>) {
    println!("Destroying box that contains {}", value); // value is destroyed here, and memory gets freed
}

// This function borrows the value by reference
fn borrow(reference: &i32) {
    println!("This is: {}", reference);
}

fn main() {
    // Allocate an integer on the heap
    let boxed = Box::new(5_i32); // Value is owned by `boxed` | Lifetime of `boxed` starts 
    // Allocate an integer on the stack      
    let stacked = 6_i32; // Value is owned by `stacked` | Lifetime of `stacked` starts

    // Borrow the contents of the box. Ownership is not taken, so the contents can be borrowed again.
    borrow(&boxed); // Value is still owned by `boxed` and a reference is passed
    borrow(&stacked); // Value is still owned by `stacked` and a reference is passed

    {
        // Take a reference to the data contained inside the box
        let ref_to_boxed: &i32 = &boxed; // Value is still owned by `boxed` | Lifetime of `ref_to_boxed` starts
        // Take a copy of the value on stack
        let copy_of_stacked: i32 = stacked; // Copied value is owned by `copy_of_stacked`, original value is owned by `stacked` | Lifetime of `copy_of_stacked` starts
        // Allocate a string on the heap
        let boxed_2 = Box::new("Hello"); // Value is owned by `boxed_2` | Lifetime of `boxed_2` starts

        // Borrow `ref_to_boxed`
        borrow(ref_to_boxed); // Value is still owned by `boxed`
        // `ref_to_boxed` goes out of scope and is no longer borrowed.
        // `copy_of_stacked` and `boxed_2` is destroyed here, and memory gets freed
        
        //Lifetime of `ref_to_boxed`, `copy_of_stacked` and `boxed_2` ends
    }

    // `boxed` is now moved and hence ownership changes
    take_ownership(boxed); // Value is now owned by `take_ownership`
    // `boxed` is destroyed inside `take_ownership`, and memory gets freed
    // `stacked` is destroyed here, and memory gets freed

    //Lifetime of `boxed` and `stacked` ends
}