Step 1 - Extension method

extension StringRepeat on String {
  String repeatTimes(int n) {
    return List.filled(n, this).join();
  }
}

void main() {
  print('ha'.repeatTimes(3));
}

Step 2 - Getter on int

extension IntChecks on int {
  bool get isEven => this % 2 == 0;
}

void main() {
  print(4.isEven);
}

Step 3 - Scope and hiding

• Extensions apply when imported; name clashes resolve by hide/show or prefixing the import.
• They are static sugar: not true runtime subtyping (dynamic will not find your extension without a cast).

Good habit

• Use for ergonomics (isBlank, formatting), not for core domain rules that belong in model types.

Practice tasks

• Add extension on List<T> { T? get secondOrNull => length > 1 ? this[1] : null; } and try on [1] and [1, 2].
• Add extension on String { bool get isEmptyOrWhitespace => trim().isEmpty; } (reimplement without calling isEmpty on raw string if you want stricter whitespace-only behavior).