Question

I am trying to store functors in a stl map and then call it one by one , but now sure how to call it. This is what I have tried so far.

#include <iostream>
#include <map>
#include <string>

class BaseFunctor {
public:
  BaseFunctor() {
  }
  ~BaseFunctor() {
  }
};

template <typename T>
class MyFunctor : public BaseFunctor {
   public:
     T operator()(T x) { 
       return x * 2;
     }
};

int main ( int argc, char**argv ) {
  std::map<std::string, BaseFunctor*> m_functorMap;

  m_functorMap.insert(std::make_pair("int", new MyFunctor<int>()));
  m_functorMap.insert(std::make_pair("double", new MyFunctor<double>()));
  m_functorMap.insert(std::make_pair("float", new MyFunctor<float>()));
  m_functorMap.insert(std::make_pair("long", new MyFunctor<long>()));

  for ( std::map<std::string, BaseFunctor*>::iterator itr = m_functorMap.begin(); itr != m_functorMap.end(); ++itr ) {
    std::cout << *(itr->second)() << std::endl;
  }


  return 0;
}

I cannot use boost

Answer 1

You have a map full of BaseFunctor*, but BaseFunctor is not callable since it has no operator(). You cannot call without casting to a pointer of a derived type, preferably with dynamic_cast. Overall it doesn’t look like a good design. You are attempting to use run-time polymorphism where it can’t.