How a C++ factory pattern may be applied to subclasses using some static methods.

cpp_factory_w_statics.cpp

#include <iostream>
#include <vector>

class Base {
  public:
  Base() {}
  virtual int func() = 0;
};

class Sub1 : public Base {
  public:
  using Base::Base;
  int func() override { return 1; };

  static Base* create() { return new Sub1(); }
  static bool check() { return false; }
};

class Sub2 : public Base {
 public:
  using Base::Base;
  int func() { return 2; };
  static Base* create() {
    return new Sub2();
  }
  static bool check() {
    return true;
  }
};

void dobase(Base* b) {
  std::cout << b->func() << std::endl;
}

int main(void) {

  Sub1 s1;
  Base* s2 = Sub2::create();

  std::vector<Base*> v({
    &s1, s2
  });

  for ( auto it: v ) {
    std::cout << it->func() <<std::endl;
  }

  // pretty easy to make a factory around this
  std::vector<std::pair<Base* (*)(), bool (*)()>> chooser(
      {std::make_pair(Sub2::create, Sub2::check),
       std::make_pair(Sub1::create, Sub1::check)});

  for (auto it : chooser) {
    if ( it.second() ) {
      Base* b = it.first();
      dobase(b);
    }
  }

  return 0;
}

Better examples here https://stackoverflow.com/questions/5450742/is-it-possible-in-c-to-loop-over-all-subclasses-of-an-abstract-class