Composed Interface class

Question

Is there any right way to declare a class (interface) Limit that can be used as "composition" of both interfaces Param and Lim?

Base interface classes Param and Lim:

class Param {
public:
    virtual char *toStr(void) = 0;
};

class Lim {
public:
    virtual char *toStrL(void) = 0;
};

ParamA and ParamB implements interface Param:

class ParamA : public Param {
public:
    virtual char *toStr(void){ return "A";};    
};

class ParamB : public Param {
public:
    virtual char *toStr(void){ return "B";} 
};

LimitA and LimitB additionally implements Lim:

class LimitA : public ParamA, public Lim {
public:
    virtual char *toStrL(void){ return "LA";}
};

class LimitB : public ParamB, public Lim {
public:
    virtual char *toStrL(void){ return "LB";}
};

With Limit I would like to access methods toStr() and toStrL()

class Limit : public Param, public Lim {
};

void example(void){
    LimitA limitA;
    LimitB limitB;
    Limit *limit = polymorphic_downcast<Limit *>(&limitB);  // unable to type cast correctly
    char *str1 = limit->toStr();
    char *str2 = limit->toStrL();
}

Answer 1

No, that's not possible. The runtime can only know about derived classes you explicitly inherited from in the class declaration. You cannot insert extra classes later.