TypeScript snippets

Shape.ts

type Shape =
    { kind: "circle", radius: number } |
    { kind: "rectangle", w: number, h: number } |
    { kind: "square", size: number };

function assertNever(obj: never) {
    throw new Error("Unexpected object");
}

function getArea(shape: Shape) {
    switch (shape.kind) {
        case "circle":
            return Math.PI * shape.radius ** 2;
        // case "rectangle":
        //     return shape.w * shape.h;    
        case "square":
            return shape.size ** 2;    
    }

    assertNever(shape);
}

const shape: Shape = { kind: "circle", radius: 10 };
const area = getArea(shape);