Dart 可选类型扩展

    final String? a = null;
    DDLog(a.runtimeType); // Null
    DDLog(a.or(() => "456")); // 456
    DDLog(a.or((){
      return "111";
    })); // 111

extension GetDynamicExt<T> on T {

  /// 返回可选值或者 `else` 闭包返回的值
  /// 例如. nullable.or(else: {
  /// ... code
  /// })
  T or(T Function() block) {
    return this ?? block();
  }
}