Solution to var problem using extension methods in Dart

var_problem_extension_solution.dart

void main() {
  final list = <int>[1, 2, 3, 4, 2, -1, 5];
  final maxValue = 12;
  
  final sum = list.clampedSum(maxValue);
  
  /// ... more code that uses `sum` ...
}

extension ClampedAdder on List<int> {
  int clampedSum(int maxValue) {
    var sum = 0;
    for(final val in this) {
      sum += val;
    }
    if(sum > maxValue) {
      sum = maxValue;
    }
    return sum;
  }
}