Question about T=Self

I am quite new to Rust. I don't understand the code below. The problem is the definition of the trait Add. I don't know the meannig of the suffix<T=Self>. I know the meaning of Self: This is the type of the current object. For example Self is Pointin fn add(&self, other:&(i32,i32))->Self in impl Add<(i32,i32)> for Point.
But I don't understand why this suffix is necessary for the compilation.

struct Point<T>{
trait Add<T=Self>
    fn add(&self, other:&T)->Self;

impl Add<(i32,i32)> for Point<i32>
    fn add(&self, other:&(i32,i32))->Self
        Point{x:self.x+other.0, y:self.y+other.1}
fn main()


It's a default for the type parameter.

It means you can refer to Add without any type parameters and it will assume T is Self, or you can specify it manually like Add<u64> and then the default value is ignored.

Since a lot of arithmetic operations end up being mostly used in contexts where both operands are the same type, it can be convenient to not have to specify T.


For example, if you want to implement Point + Point, you can simply write

impl Add for Point { /* ... */ }

and it's equivalent to explicitly writing

impl Add<Point> for Point { /* ... */ }

or indeed

impl Add<Self> for Point { /* ... */ }