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.
1 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.
2 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.
3 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.