不允许使用指向不完整类类型的指针的类类型向量的前向声明

I have two classes, foo and bar. foo includes bar and contains a std::vector of pointers to bar objects. at some point during runtime, bar has to access this vector of pointers to other bar objects. Therefor, foo contains a method named getBarObjects() that returns the array of pointers.I have two classes, foo and bar. foo includes b