将引用包装器的向量转换为基类，将reference_wrapper的向量转换为派生类，则无法动态转换

Question

As in title. I got this error when trying to dynamic_cast

cannot dynamic_cast '(& obj)->std::reference_wrapper<_Tp>::get()' (of type 'class MEPObject') to type 'class MEPGene&' (target is not pointer or reference to complete type) genes.push_back(dynamic_cast (obj.get()));

class MEPObject;
class MEPGene;
typedef std::vector<std::reference_wrapper<MEPObject>> MEPObjects;
typedef std::vector<std::reference_wrapper<MEPGene>> MEPGenes;

void dynamicCast(MEPObjects &objects, MEPGenes &genes)
{
    for(const auto &obj: objects)
    {
        genes.push_back(dynamic_cast<MEPGene&> (obj.get()));
    }
}

Answer 1

Forward declaration is not enough.

Definition of MEPGene is required (to see inheritance).