I am wondering whether it is possible to have an operator in a non-templated parent class with an auto return value and a templated child class??

Here is an example:

#include <vector>
#include <iostream>
class parent{
public:
  virtual ~parent(){};
  auto & operator()(const int i);
};
template<typename T>
class child:public parent{
protected:
  std::vector<T> X_;
public:
  child(std::vector<T> const &X):X_{X}{};
  T & operator()(const int i){
    return(X_[i]);
  }
};
auto & parent::operator()(const int i){
  if(auto * x=dynamic_cast<child<int>*>(this)){
    return((*x)(i));
  }else if(auto * x=dynamic_cast<child<double>*>(this)){
    return((*x)(i));
  }else{
    throw std::string("error");
  }
};
int main(){
  child Y1(std::vector<int>{5,10});
  child Y2(std::vector<double>{6,11});
  std::cout<<Y1(0)<<std::endl;
  parent * X=&Y1;
  std::cout<<(*X)(0)<<std::endl;
}

Currently I get: error: 'auto' in return type deduced as 'double' here but deduced as 'int' in earlier return statement

Any suggestions much appreciated.