Write a Function to Compute Shape Area

TypeScript

Technical Specification

Using the Shape type, implement a function that returns the area of either a circle or a rectangle.

Input/Output Samples

Input:{ kind: "circle", radius: 2 }

Output:12.566...

Optimal Logic Path

function area(shape: { kind: "circle"; radius: number } | { kind: "rectangle"; width: number; height: number }) {
  switch (shape.kind) {
    case "circle":
      return Math.PI * shape.radius * shape.radius;
    case "rectangle":
      return shape.width * shape.height;
  }
}

Architectural Deep-Dive

Control flow narrowing lets TypeScript infer the correct shape type inside each switch case.