any_wrapper.cpp

#include <iostream>
#include <boost/any.hpp>
#include <complex>

struct Any{
  boost::any any_;

  template <class T>
  Any(T const& x):any_(x){}
  template <class T>
  Any& operator=(T const& x){ any_ = x; return *this;}

  template <class T>
  operator T() const{ return boost::any_cast<T>(any_);}
};

#define Print(name) (std::cout << #name << " = " << name << std::endl)

int main()
{
  Any a = 42; // int

  int i = a;
  Print(i);

  a = 3.14; // double
  double d = a;
  Print(d);

  // i = a; // FAIL to cast (double to int), and throw runtime error

  a = std::complex<double>(0.0,1.0);  // complex
  std::complex<double> z = a;
  Print(z);
  
  // d = a; // FAIL to cast (complex to double), and throw runtime error

  return 0;
}