cpp-variant/include/variant/detail/helper.hpp

#pragma once

namespace variant { namespace detail {
  template <typename... Ts> struct helper;

  template <typename F, typename... Ts> struct helper<F, Ts...> {
    inline static void destroy(size_t id, void * data) {
      if (id == sizeof...(Ts)) {
        reinterpret_cast<F *>(data)->~F();
      } else {
        helper<Ts...>::destroy(id, data);
      }
    }

    inline static void move(size_t old_t, void * old_v, void * new_v) {
      if (old_t == sizeof...(Ts)) {
        new (new_v) F(std::move(*reinterpret_cast<F *>(old_v)));
      } else {
        helper<Ts...>::move(old_t, old_v, new_v);
      }
    }

    inline static void copy(size_t old_t, const void * old_v, void * new_v) {
      if (old_t == sizeof...(Ts)) {
        new (new_v) F(*reinterpret_cast<const F *>(old_v));
      } else {
        helper<Ts...>::copy(old_t, old_v, new_v);
      }
    }
  };

  template <> struct helper<> {
    inline static void destroy(size_t, void *) {}
    inline static void move(size_t, void *, void *) {}
    inline static void copy(size_t, const void *, void *) {}
  };
}}