#include <iostream>

struct MyUnion
{
public:
  union {
    bool bool_value;
    int int_value;
    float float_value;
  };
};

template<typename T> T parse(const MyUnion& h)
{
  T t;

  if (typeid(T) == typeid(bool)) {
    t = h.bool_value;
  } else if (typeid(T) == typeid(int)) {
    t = h.int_value;
  } else if (typeid(T) == typeid(float)) {
    // t = h.float_value; // see **Warning** below; use float specialization instead
  }

  return t;
}

// 'float' template specialization to avoid conversion warning.
template<> float parse(const MyUnion& h)
{
  return h.float_value;
}

int main()
{
  MyUnion mu1; mu1.bool_value = true;
  MyUnion mu2; mu2.int_value = 42;
  MyUnion mu3; mu3.float_value = 3.14159;

  std::cout << "As bool: "  << parse<bool>(mu1)  << std::endl;
  std::cout << "As int: "   << parse<int>(mu2)   << std::endl;
  std::cout << "As float: " << parse<float>(mu3) << std::endl;
}

// **Warning**
// In function 'T parse(const Heterogeneous&) [with T = int]':
// Line 22: warning: converting to 'int' from 'const float'

As bool: true
As int: 42
As float: 3.14159