c – 在调用过程中删除std :: function

在调用过程中,是否要销毁/删除std :: function是未定义的行为？

class Event {
  public:
    Event(std::function<void()> f) : func(std::move(f)) {}
    ~Event() {}
    std::function<void()> func;
};

int main()
{
    std::vector<Event> events;
    auto func = [&]() {
      events.pop_back();  
      std::cout << "event" << std::endl;
      // do more work  
    };

    events.emplace_back(std::move(func));
    events[0].func();

    return 0;
}

解决方法

这是 [res.on.objects]p2未定义的：

If an object of a standard library type is accessed,and the beginning
of the object’s lifetime does not happen before the access,or the
access does not happen before the end of the object’s lifetime,the
behavior is undefined unless otherwise specified.

在这种情况下,“访问”包括对std :: function的函数调用操作符的调用. std :: function对象的生命周期在pop_back()调用结束时,在访问过程中结束.因此,访问不会在对象生命周期结束之前发生,并且行为未定义.