如何为Dart静态扩展指定泛型类型？

extension ListExtension<T> on List<T> {
  List<T> filter(bool Function(T) test) {
    var result = <T>[];
    for (var item in this) {
      if (test(item)) {
        result.add(item);
      }
    }
    return result;
  }
}

void main() {
  var numbers = [1, 2, 3, 4, 5];
  var evenNumbers = numbers.filter((n) => n % 2 == 0);
  print(evenNumbers); // 输出 [2, 4]
}

extension NumberListExtension<T extends num> on List<T> {
  List<T> filter(bool Function(T) test) {
    var result = <T>[];
    for (var item in this) {
      if (test(item)) {
        result.add(item);
      }
    }
    return result;
  }
}

void main() {
  var numbers = [1, 2, 3, 4, 5];
  var evenNumbers = numbers.filter((n) => n % 2 == 0);
  print(evenNumbers); // 输出 [2, 4]
  
  var strings = ['hello', 'world'];
  // strings.filter((s) => s.length > 3); // 编译错误，String不满足泛型约束
}