problem with polymorphism

Hello,
I am trying to write a function that transform a une subclass into a different one (both inherited from the same virtual parent).

class Parent{
public:
~Parent() = 0;
virtual bool isChild1() const = 0;
void changeChild();
private:
}

class Child1 : public Parent{
public:
~Child1(){};
bool isChild1(){return true;}
private:
// some int
}

class Child2 : public Parent{
public:
~Child2(){};
bool isChild1(){return false;}
private:
// some other int
}

Let me assume I have a vector of <Parent*> what's the right way to implement changeChild so that i can mutate from Child2 to Child1 (or viceversa)?

std::vector<Parent*> v{};
// initalize v with appropriate Childs;
for (int i = 0;i<v.size();++i){
if (v[i]->isChild1()){
v[i].changeChild()
}
}
// ideally now all the vector elements are pointers to Child2

What I'd like to do is something like

void Parent::changeChild(){
if(this->isChild1()){
// create a new pointer to a Child2 and point this to it
}else{
// create a new pointer to a Child1 and point this to it
}
//somehow destroy the original this. 
}

I have problems as in the function definition I cannot point "this" to something else.

Is there any workaround for this kind of operation? Thanks.

keskiverto (10402)

I have merely a faint recollection that something like this might apply:

std::vector<Parent*> v{};
// initalize v with appropriate Childs;

for ( auto & p : v ) {
  if ( auto c1 = dynamic_cast<Child1*>( p ) ) {
    Child2* c2 = new Child2 // initialize *c2 or copy appropriate bits from *c1
    delete p;
    p = c2;
  }
}

ericM (48)

which is cool, I managed to understand your answer and use a less elegant version for my problem, check for memory leaking and be happy.
Agan on topic, I am trying to overload the >> operator for the Parent class, so that I'll be able, for example, to read data from file.

I defined in the Parent.hpp file the function

std::istream& operator>>(std::istream& is, Parent* var){
  bool isChild1;
  is>>isChild1;
  if(isChild1){
    //define Child1 vars
    is >> vars;
    if(!is)return is;
    Child1 *pippo = new Child1(vars);
    var = pippo;
    return is
    }else{
    //define Child2 vars
    is >> vars;
    if(!is)return is;
    Child2 *pippo = new Child2(vars);
    var = pippo;
    return is;
    }
  }

The compiler does not complain, but I am not confident this bit of code is safe. Is there a better way to define an >> operator to read either Child1 or Child2 dynamically from file?
Thanks in advance.

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problem with polymorphism