rust-intro: borrow

rust-intro-borrow.rs

// http://rustbyexample.com/scope/borrow.html
// https://is.gd/E0jeLL

fn simple_borrow() {

    let mut v = vec!["A"];

    {
        // immutable borrow
        let borrow = &v;
        // borrow.push("B");
    }

    {
        // mutable borrow
        let mut borrow = &mut v;
        borrow.push("C");
    }
    v.push("D");

    println!("{:?}", v);
}


fn take_and_print(vec: Vec<i32>) {
    for elem in vec.iter() {
        println!("{}", elem)
    }

    // vec goes out of scope and it is taken
}

fn borrow_and_print(vec: &Vec<i32>) {
    for elem in vec.iter() {
        println!("{}", elem)
    }

    // vec borrow goes out of scope and ownership is returned
}

fn try_brrow_and_destory() {
    let mut v = vec![1, 2, 3];
    borrow_and_print(&v);
    v.push(4);

    take_and_print(v);
    v.push(5);
}

// This function takes ownership of a box and destroys it
fn eat_box_i32(boxed_i32: Box<i32>) {
    println!("Destroying box that contains {}", boxed_i32);
}

// This function borrows an i32
fn borrow_i32(borrowed_i32: &i32) {
    println!("This int is: {}", borrowed_i32);
}

fn advanced_borrow() {
    // Create a boxed i32, and a stacked i32
    let boxed_i32 = Box::new(5_i32);
    let stacked_i32 = 6_i32;

    // Borrow the contents of the box. Ownership is not taken,
    // so the contents can be borrowed again.
    borrow_i32(&boxed_i32);
    borrow_i32(&stacked_i32);

    {
        // Take a reference to the data contained inside the box
        let _ref_to_i32: &i32 = &boxed_i32;

        // Error!
        // Can't destroy `boxed_i32` while the inner value is borrowed.
        // eat_box_i32(boxed_i32);
        // FIXME ^ Comment out this line

        // `_ref_to_i32` goes out of scope and is no longer borrowed.
    }

    // `boxed_i32` can now give up ownership to `eat_box` and be destroyed
    eat_box_i32(boxed_i32);
}

fn main() {

    simple_borrow();
    try_brrow_and_destory();
    advanced_borrow();

}