Derive Macro derive_more::AddAssign

#[derive(AddAssign)]

Available on crate feature add_assign only.

What #[derive(AddAssign)] generates

This code is very similar to the code that is generated for #[derive(Add)]. The difference is that it mutates the existing instance instead of creating a new one.

Tuple structs

When deriving AddAssign for a tuple struct with two fields like this:

#[derive(AddAssign)]
struct MyInts(i32, i32);

Code like this will be generated:

impl ::core::ops::AddAssign for MyInts {
    fn add_assign(&mut self, rhs: MyInts) {
        self.0.add_assign(rhs.0);
        self.1.add_assign(rhs.1);
    }
}

The behaviour is similar with more or less fields.

Regular structs

When deriving for a regular struct with two fields like this:

#[derive(AddAssign)]
struct Point2D {
    x: i32,
    y: i32,
}

Code like this will be generated:

impl ::core::ops::AddAssign for Point2D {
    fn add_assign(&mut self, rhs: Point2D) {
        self.x.add_assign(rhs.x);
        self.y.add_assign(rhs.y);
    }
}

The behaviour is similar with more or less fields.

Enums

Deriving AddAssign is not (yet) supported for enums. This is mostly due to the fact that it is not trivial convert the Add derivation code, because that returns a Result<EnumType> instead of an EnumType. Handling the case where it errors would be hard and maybe impossible.