In object_pool.h, line 48, there is a struct with a union in it:

  struct LinkedList {
    union {
      LinkedList* next{nullptr};
      T t;
    };
  };

In my environment (VS2013), the compiler cannot accept a union containing a class with a copy constructor. Can I remove the union definition, such as

  struct LinkedList {
      LinkedList* next{nullptr};
      T t;
  };

, or I must use boost::variant to replace it?