Rust Programming By Example

Playing with mutable borrows

The first one works just like OpenOptions:

struct Number(u32);

impl Number {
    fn new(nb: u32) -> Number {
        Number(nb)
    }

    fn add(&mut self, other: u32) -> &mut Number {
        self.0 += other;
        self
    }

    fn sub(&mut self, other: u32) -> &mut Number {
        self.0 -= other;
        self
    }

    fn compute(&self) -> u32 {
        self.0
    }
}

If you wonder about self.0, just remember that it's how you access a tuple field.

And then you can call it as follow:

let nb = Number::new(0).add(10).sub(5).add(12).compute();
assert_eq!(nb, 17);

This is the first way to do it.

You'll note that you need to add an ending method so that you can transform your mutable borrow into an object (otherwise, you'll have a borrow issue).

Let's now take a look at the second way to ...