DART

dart extension function

extension NumberParsing on String {
  int parseInt() {
    return int.parse(this);
  }
  // ···
}

dart extension

extension FancyNum on num {
  num plus(num other) => this + other;

  num times(num other) => this * other;
}

extension function flutter

extension NumberParsing on String {
  int parseInt() {
    return int.parse(this);
  }
  // ···
}