Operator overloading and mixins

We'll take a look at two more Dart features that are useful in some situations but aren't crucial when using Dart, and you'll probably not use them on a daily basis.

Operator overloading

Dart lets us overload its default behavior when using standard operators such as ==, +, -, [], or []=. A typical use case is when using 2D/3D vectors:

class Vector {
  int x, y;
  Vector(this.x, this.y);
  
  operator ==(Vector v) => this.x == v.x && this.y == v.y;
  operator  +(Vector v) => new Vector(this.x + v.x, this.y + v.y);
  operator  -(Vector v) => new Vector(this.x - v.x, this.y - v.y);
}

We can use unit testing to check whether operators work as expected:

var v1 = new Vector(5, 3);
var v2 = new Vector(7, 2);

Vector v3 = v1 + v2;
expect(v3.x, 12);
expect(v3.y, 5);

expect((v1 - v2) == new Vector(-2, 1), isTrue);

var v6 = new Vector(3, 5);
expect(v1 == v6, isFalse);

Unlike JavaScript, there's no === operator (three equal signs) in Dart that compares variables...