Re: c++ compiler results

[Plinky Dermis <plinkydermis at hotmail dot com>]

#include <exception>
#include <iostream>
#include <string>
#include <tuple>
#include <typeinfo>

// goal: make this code work with constexpr, tested on g++ 4.7.2 (-std=c++11)


//#define constexpr


std::string operator"" _s(const char *literal_string, size_t chars)
{
  return std::string(literal_string, chars);
}


template <typename T,typename U>
constexpr bool typematch(const T& a, const U& b)
{
  return typeid(a) == typeid(b);
}


template <size_t N>
struct MatchTypes_t
{
  MatchTypes_t() = default;


  template<typename M,typename ...T>
  constexpr const void *matchType(const M& match, const std::tuple<T...>& t) const
  {
    const size_t tsize = std::tuple_size<std::tuple<T...>>::value;
    if (typematch(std::get<tsize-N>(t), match)) {
      constexpr auto find = MatchTypes_t<N-1>();
      return find.matchType(match, t)
        ? nullptr : static_cast<const void*>(&(std::get<tsize-N>(t)));
    } else {
      constexpr auto find = MatchTypes_t<N-1>();
      return find.matchType(match, t);
    }
  }
};


template <>
struct MatchTypes_t<0>
{
  template<typename M,typename ...T>
  constexpr const void *matchType(const M& match, const std::tuple<T...>& t) const
  {
    return nullptr;
  }
};


namespace std {


template <typename M,typename ...T>
const M& get(std::tuple<T...>& t, std::exception e = std::bad_typeid(), M dummy = M()) throw(std::exception)
{
  const size_t tsize = std::tuple_size<std::tuple<T...>>::value;
  constexpr auto find = MatchTypes_t<tsize>();
  constexpr const void *ptr = find.matchType(dummy, t);
  if (!ptr) { // static_assert(ptr, "bad_typeid or more than one of that type");
    throw e;
  }
  return *(static_cast<const M*>(ptr));
}


} // namespace std


int main()
{
  auto vary = std::make_tuple('A', "mixed set of"_s, -1.2, 2);

  const auto &s = std::get<std::string>(vary);
  const auto d = std::get<double>(vary);
  return ((s == "mixed set of") && (d == -1.2)) ? 0 : 1;
}