// Basic form
type Numeric extends string|float|int;

// Type casts
type Numeric extends string|float|int {
  public static function cast(parent $in): self {
    is_numeric($in) || throw new ClassCastException($in.' is not numeric');
    return $in;
  }
}

$times= (Numeric)($argv[1] ?? 10);

// Extension methods
type User extends array<string, mixed> {
  public function id(): UUID { return new UUID($this['_id']); }
  public function name(): string { return $this['name']; }
}

$admin= (User)['_id' => '691522c4-2f24-4264-ba75-4df62b931422', 'name' => 'Admin'];
$admin->id();  // util.UUID{691522c4-2f24-4264-ba75-4df62b931422}