inheritance - c++ typecast base ptr to derived ptr held in a reference class -


i'm trying create object reference template class hold class pointers , works except when trying type cast base class ptr derived class ptr.

here code:

#include <stdio.h> #include <stdlib.h>  #define null nullptr  class basetype; class derivedtype;  template<class t> class objref { public:   t *ptr = null;  //should private    objref& operator= (t *ptr) { this->ptr = ptr; return *this; }   objref& operator= (const objref &ref) { ptr = ref.ptr; return *this; }   operator t*() const {return ptr;}   operator t() const {return *ptr;}   objref() {}   objref(const objref &copy) { ptr = copy.ptr; } #ifdef void_fix   objref(void*p) { ptr = (t*)p; }  //this fix bug except not work multiple inheritance , not safe #else   objref(t*p) { ptr = p; } #endif   ~objref() { }   t* operator->() const {return ptr;}  //unfortunately operation. (dot) can not overloaded - make life easy :( };  class object {};  class basetype : public object { public:   int basevalue; };  class derivedtype : public basetype { public:   operator basetype*() {return (basetype*)this;}  //helpful?   int derivedvalue; };  typedef objref<basetype> base; typedef objref<derivedtype> derived;  void func4(base x) {   x->basevalue = 1; }  void func5(derived x) {   x->derivedvalue = 1; }  int main() {   base b = null;   derived d = null;   base x;    x = d;  //no type cast needed   func4((base)d);  //cast derived base class - no problem    b = d;  //base point derived //  func5((derived)b);  //cast base derived - not work (desired syntax)   // gcc -fpermissive can used change error warning - can silence warning ?   // cl.exe equivalent be?  //  func5((derived)b.ptr);  //invalid cast, ptr should private //  func5((derivedtype*)b);  //invalid cast, ptr should private //  func5(dynamic_cast<derivedtype*>(b.ptr));  //invalid cast, source type not polymorphic, ptr should private    func5((derivedtype*)b.ptr);  //this works undesired , ptr should private   func5(static_cast<derivedtype*>(b.ptr));  //works again undesired , ptr should private    return 0; }

in example objref<> template holds pointer class defined , used new type. works fine except trying cast base class derived class. @ how func5() being called base class reference. first attempt desired syntax. if use ptr inside reference class work undesired.

i feel i'm missing operator or something.

thanks.

as usual found solution moments after posting.
objref<> class needs know base class. here new code:

#include <stdio.h> #include <stdlib.h>  #define null nullptr  class basetype; class derivedtype;  template<class t> class objref { public:   t *ptr = null;    objref& operator= (auto *ptr) { this->ptr = ptr; return *this; }   objref& operator= (const objref<auto> &ref) { ptr = ref.ptr; return *this; }   operator t*() const {return ptr;}   objref() {}   objref(const objref<auto> &copy) { ptr = (t*)copy.ptr; }   objref(t*p) { ptr = p; }   ~objref() { }   t* operator->() const {return ptr;}  //unfortunately operator. (dot) can not overloaded - make life easy :( };  class object {};  class basetype : public virtual object { public:   int basevalue; };  class interfacetype : public virtual object { public:   virtual void func7() {     printf("it works!\n");   }; };  typedef objref<interfacetype> interface;  class derivedtype : public basetype, public interfacetype { public:   int derivedvalue; };  typedef objref<basetype> base; typedef objref<derivedtype> derived;  void func4(base x) {   x->basevalue = 1; }  void func5(derived x) {   x->derivedvalue = 2; }  void func6(interface x) {   x->func7(); }  int main() {   base b = new basetype();   derived d = new derivedtype();   base x;    x = d;  //no type cast needed   func4((base)d);  //cast derived base class - no problem   printf("basevalue=%d\n", d->basevalue);    b = d;  //base point derived   func5((derived)b);  //cast base derived - works now!   printf("derivedvalue=%d\n", d->derivedvalue);    func6(d);    return 0; }

update : posted new version work level of inheritance requires c++14 (auto keyword)

update #2 : uses single objref class (still requires c++14). unfortunately cl.exe doesn't support 'auto' template parameters yet :(

update #3 : added test code prove works.


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