Challenge 2 — Solution

Task: Create a Shape interface with a getArea() method, two
implementations (Circle, Square), and a ShapeFactory with a static
create(string $type, ...$args) method using match() to construct the
right one. Create one of each via the factory and echo their areas.

<?php
    interface Shape {
        public function getArea(): float;
    }

    class Circle implements Shape {
        public function __construct(private float $radius) {}
        public function getArea(): float {
            return pi() * $this->radius ** 2;
        }
    }

    class Square implements Shape {
        public function __construct(private float $side) {}
        public function getArea(): float {
            return $this->side ** 2;
        }
    }

    class ShapeFactory {
        public static function create(string $type, ...$args): Shape {
            return match ($type) {
                'circle' => new Circle(...$args),
                'square' => new Square(...$args),
                default => throw new InvalidArgumentException("Unknown shape type: $type"),
            };
        }
    }

    $circle = ShapeFactory::create('circle', 5);
    $square = ShapeFactory::create('square', 4);

    echo "Circle area: " . round($circle->getArea(), 2) . "<br>";
    echo "Square area: " . $square->getArea();
?>


Output:
Circle area: 78.54
Square area: 16

Notes:
- ...$args (the "splat" operator) collects any number of extra
  arguments passed to create() into an array, then new Circle(...$args)
  "unpacks" them back out as individual constructor arguments - letting
  one factory method handle constructors with genuinely different
  parameter counts (Circle takes 1 arg, and a more complex shape could
  take more) without ShapeFactory needing to know each shape's specific
  signature in advance.
- Calling code never references Circle or Square directly - it only
  ever interacts with ShapeFactory::create() and the returned Shape
  interface, exactly the decoupling benefit the chapter's own
  NotificationFactory example demonstrated.
- match() throws a clear InvalidArgumentException for any unrecognised
  $type, exactly mirroring the chapter's own NotificationFactory
  pattern for handling an unknown value.