Tagged unions / sealed classes #107

// Declaration
enum Distance {
  case Kilometers(public int $km);
  case Miles(public int $miles);
}

// Usage
$walk= Distance::Miles(500);
print $walk->miles; // prints "500"

// Declaration
enum Optional {
  case None {
    public function bind(callable $f) { return $this; }
    public function value(): mixed { return null; }
  };
 
  case Some(private mixed $value) {
    public function bind(callable $f): Optional { return Optional::of($f($this->value)); }
    public function value(): mixed { return $this->value; }
  };

  public static function of($value): self {
    return $value instanceof self ? $value : ($value ? self::Some($value) : self::None);
  }
}

// Usage
$value= Optional::of($record)->bind(fn($r) => $r['distance'] + 1)->value();