Notes

Exhaustiveness checking:

type Shape = Circle | Square;
 
function getArea(shape: Shape) {
  switch (shape.kind) {
    case "circle":
      return Math.PI * shape.radius ** 2;
    case "square":
      return shape.sideLength ** 2;
    default: {
      const exhaustiveCheck: never = shape;
      return exhaustiveCheck;
    }
  }
}

Typecasting is evil.

If you want to represent an empty object, use Record<string, never>.