Casting from an abstract base class reference to derived class reference - c++

Question

I have following C++ code
AbstractClass_01.h
class AbstractClass_01 {
public:
virtual void method_01() = 0;
};
AbstractClass_02.h
class AbstractClass_02 {
public:
virtual void method_02() = 0;
};
ClassA.h
#include "AbstractClass_02.h"
class ClassA : public AbstractClass_02{
public:
void method_02();
void method_03();
};
ClassA.cpp
#include "ClassA.h"
void ClassA::method_02() {}
void ClassA::method_03() {}
ClassB.h
#include "AbstractClass_01.h"
#include "AbstractClass_02.h"
class ClassB : public AbstractClass_01 {
public:
ClassB(AbstractClass_02& _obj);
void method_01();
private:
AbstractClass_02 &obj;
};
ClassB.cpp
#include "ClassB.h"
#include "ClassA.h"
ClassB::ClassB(AbstractClass_02& _obj) : obj(_obj) {}
void ClassB::method_01() {
static_cast<ClassA&>(obj).method_03();
}
main.cpp
#include "ClassA.h"
#include "ClassB.h"
int main(int argc, char** argv) {
ClassA a;
ClassB b(a);
b.method_01();
return 0;
}
My question is whether the casting which I have done in the ClassB::method_01 is common C++ construct whether it is a sign of wrong design?
EDIT:
The reason why the ClassB constructor accepts references to the AbstractClass_02 instead of the ClassA is that I need to pass references to various objects which all have common interface AbstractClass_02. The problem is that this interface doesn't contain the method_03. One possible solution could be to append that method into the interface AbstractClass_02 but that method isn't cohesive with the method_02.

Answer 1

This is known as downcasting and is typically a sign of bad design. Based on the limited knowledge we have, it seems obvious that you should take ClassA in constructor instead of AbstractClass_01
#include "AbstractClass_01.h"
#include "ClassA.h"
class ClassB : public AbstractClass_01 {
public:
ClassB(ClassA & _obj);
void method_01();
private:
ClassA &obj;
};
But we don't know your real problem and why did you decide to go with casting or accepting interface in the first place.