drawShape.ts

type Rectangle = {
  kind: "rectangle";
  width: number;
  height: number;
};

type Circle = {
  kind: "circle";
  radius: number;
};

type Triangle = {
  kind: "triangle";
  base: number;
};

type Oval = {
  kind: "oval";
  width: number;
  height: number;
};

function drawShape(shape: Circle | Rectangle | Triangle | Oval): number {
  if (shape.kind === "circle") {
    return shape.radius;
  }
  if (shape.kind === "rectangle") {
    return shape.height * shape.width;
  }
  if (shape.kind === "triangle") {
    return shape.base;
  }
  if (shape.kind === 'oval') {
    return shape.height * shape.width;
  }
  expectNever(shape);
}

function expectNever(_nev: never): never {
  throw new Error("Unexpected never");
}