Aliasing - Rust By Example
Description: A description

# Aliasing

Data can be immutably borrowed any number of times, but while immutably borrowed, the original data can't be mutably borrowed. On the other hand, only one mutable borrow is allowed at a time. The original data can be borrowed again only after the mutable reference has been used for the last time.

    struct Point { x: i32, y: i32, z: i32 }

    fn main() {
        let mut point = Point { x: 0, y: 0, z: 0 };

        let borrowed_point = &point;
        let another_borrow = &point;

        // Data can be accessed via the references and the original owner
        println!("Point has coordinates: ({}, {}, {})",
                    borrowed_point.x, another_borrow.y, point.z);

        // Error! Can't borrow `point` as mutable because it's currently
        // borrowed as immutable.
        // let mutable_borrow = &mut point;
        // TODO ^ Try uncommenting this line

        // The borrowed values are used again here
        println!("Point has coordinates: ({}, {}, {})",
                    borrowed_point.x, another_borrow.y, point.z);

        // The immutable references are no longer used for the rest of the code so
        // it is possible to reborrow with a mutable reference.
        let mutable_borrow = &mut point;

        // Change data via mutable reference
        mutable_borrow.x = 5;
        mutable_borrow.y = 2;
        mutable_borrow.z = 1;

        // Error! Can't borrow `point` as immutable because it's currently
        // borrowed as mutable.
        // let y = &point.y;
        // TODO ^ Try uncommenting this line

        // Error! Can't print because `println!` takes an immutable reference.
        // println!("Point Z coordinate is {}", point.z);
        // TODO ^ Try uncommenting this line

        // Ok! Mutable references can be passed as immutable to `println!`
        println!("Point has coordinates: ({}, {}, {})",
                    mutable_borrow.x, mutable_borrow.y, mutable_borrow.z);

        // The mutable reference is no longer used for the rest of the code so it
        // is possible to reborrow
        let new_borrowed_point = &point;
        println!("Point now has coordinates: ({}, {}, {})",
                 new_borrowed_point.x, new_borrowed_point.y, new_borrowed_point.z);
    }