Step 1 - Generic swap

(T, T) swap<T>(T a, T b) {
  return (b, a);
}

Step 2 - Use swap with different types

void main() {
  var (a, b) = swap<int>(10, 20);
  print('$a, $b'); // 20, 10

  var (x, y) = swap<String>('left', 'right');
  print('$x, $y'); // right, left
}

Step 3 - Generic firstOrNull

T? firstOrNull<T>(List<T> items) {
  if (items.isEmpty) return null;
  return items.first;
}

void main() {
  print(firstOrNull<int>([5, 6, 7]));
  print(firstOrNull<String>([]));
}

Why this matters

• One function works for many types.
• Type safety is preserved without dynamic.

Practice tasks

• Write T? lastOrNull<T>(List<T> items).
• Write List<T> twice<T>(T value) returning [value, value].
• Call these with int, String, and bool.