Unions and Narrowing 28 exercises

Transcript

00:00 Okay, we are back with our calculateArea function. We have a square and a circle again, and we have added, though, a new test case. This new test case is right down the bottom here. And in our previous test cases, we're checking if you pass a kindCircle or a kindSquare,

00:17 then it should calculate the area properly using a discriminated union. But down here in the calculateArea function, it should calculate the radius when we don't pass in a member of the discriminated union, when we don't pass in a kind. So here we're sort of implicitly

00:32 saying when you don't pass a kind, you should treat it as if it were a circle. So here we're kind of like expecting a default behavior from our discriminated union. Hmm, interesting. Your job here is to try to find a way to express this, first of all, on the type level. So

00:50 in these types up here, you'll also probably need to change around some of the stuff in the function body to get the narrowing working in there. Good luck.

Problem

Adding Defaults to a Discriminated Union

We're back to the calculateArea function example:


function calculateArea(shape: Shape) {
  if (shape.kind === "circle") {
    return Math.PI * shape.radius * shape.radius;
  } else {
    return shape.sideLength * shape.sideLength;
  }
}

Until now, the test cases have involved ch

Transcript

00:50 in these types up here, you'll also probably need to change around some of the stuff in the function body to get the narrowing working in there. Good luck.