Add, Mul, …

Operator overloading is implemented via traits in std::ops:

#[derive(Debug, Copy, Clone)]
struct Point { x: i32, y: i32 }
impl std::ops::Add for Point {
    type Output = Self;
    fn add(self, other: Self) -> Self {
        Self {x: self.x + other.x, y: self.y + other.y}
    }
}
fn main() {
    let p1 = Point { x: 10, y: 20 };
    let p2 = Point { x: 100, y: 200 };
    println!("{:?} + {:?} = {:?}", p1, p2, p1 + p2);
}
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Speaker Notes

Discussion points:

  • You could implement Add for &Point. In which situations is that useful?
    • Answer: Add:add consumes self. If type T for which you are overloading the operator is not Copy, you should consider overloading the operator for &T as well. This avoids unnecessary cloning on the call site.
  • Why is Output an associated type? Could it be made a type parameter?
    • Short answer: Type parameters are controlled by the caller, but associated types (like Output) are controlled by the implementor of a trait.