Re: [Boost-users] How to convert a vector of base classes to template based code?

From: Roman Perepelitsa (roman.perepelitsa_at_[hidden])
Date: 2008-07-10 08:01:58

Peng Yu <pengyu.ut <at> gmail.com> writes:
> 
> Hi,
> 
> The following program uses virtual functions. Essentially I need to go
> through all the pairs in 'v'.
> 
> Since I have already know what are in v at compile time. I would like
> to convert the dynamic polymorphism to template. Therefore, the
> runtime would be better. I think this should be done with the help of
> boost::mpl. But I'm not sure how to do it. Would you please help me?

You can use boost::fusion::vector (or boost::tuple) as a
container. You can use boost::fusion::for_each to iterate
through it (there are other algorithms in fusion of course).

#include <iostream>

#include <boost/fusion/container/vector.hpp>
#include <boost/fusion/algorithm/iteration/for_each.hpp>

struct square {
 void show_me() const {
   std::cout << "square\n";
 }
};

struct circle {
 void show_me() const {
   std::cout << "circle\n";
 }
};

struct triangle {
 void show_me() const {
   std::cout << "triangle\n";
 }
}; 

struct show {
  template <class T>
  void operator()(const T& obj) const {
    obj.show_me();
  }
};

int main() {
  using namespace boost::fusion;
  vector<square, circle, triangle, square> v;
  for_each(v, show());
}

HTH,
Roman Perepelitsa.