interoperate with any and type_erasure

[jll63]

Steven Watanabe's experiments:

#include <boost/openmethod.hpp>
#include <boost/openmethod/compiler.hpp>
#include <boost/openmethod/policies.hpp>

#include <any>
#include <boost/mp11/list.hpp>
#include <concepts>
#include <iostream>

using namespace boost::openmethod;
using namespace boost::mp11;

struct any_rtti : boost::openmethod::policies::rtti {
  template <class Class>
  static constexpr auto is_polymorphic = std::is_same_v<Class, std::any>;

  template <typename T> static type_id static_type() {
    return reinterpret_cast<type_id>(&typeid(T));
  }

  template <std::same_as<std::any> T>
  static type_id dynamic_type(const T &obj) {
    return reinterpret_cast<type_id>(&obj.type());
  }

  template <class Stream> static void type_name(type_id type, Stream &stream) {
    stream << reinterpret_cast<const std::type_info *>(type)->name();
  }

  static std::type_index type_index(type_id type) {
    return std::type_index(*reinterpret_cast<const std::type_info *>(type));
  }

  template <typename D, typename B> static D dynamic_cast_ref(B &obj) {
    return std::any_cast<D>(obj);
  }
};

struct any_policy
    : default_policy::fork<any_policy>::replace<policies::rtti, any_rtti> {};

BOOST_OPENMETHOD(foo, (virtual_<const std::any &>), void, any_policy)

// BOOST_OPENMETHOD_CLASSES(int, std::any, any_policy)
using boost::openmethod::detail::class_declaration_aux;
class_declaration_aux<any_policy, mp_list<std::any>> x;
class_declaration_aux<any_policy, mp_list<int, std::any>> y;
class_declaration_aux<any_policy, mp_list<double, std::any>> z;

BOOST_OPENMETHOD_OVERRIDE(foo, (const int &i), void) {
  std::cout << i << std::endl;
}

BOOST_OPENMETHOD_OVERRIDE(foo, (const double &d), void) {
  std::cout << d << std::endl;
}

int main() {
  boost::openmethod::initialize<any_policy>();
  std::any a(5);
  std::any d(3.14);
  foo(a);
  foo(d);
}

#include <boost/openmethod.hpp>
#include <boost/openmethod/compiler.hpp>
#include <boost/openmethod/policies.hpp>

#include <boost/type_erasure/any.hpp>
#include <boost/type_erasure/any_cast.hpp>
#include <boost/type_erasure/derived.hpp>
#include <boost/type_erasure/placeholder.hpp>
#include <boost/type_erasure/typeid_of.hpp>

#include <boost/mp11/list.hpp>

#include <iostream>

using namespace boost::openmethod;

template <typename T> constexpr bool is_any = false;
template <typename C, typename T>
constexpr bool is_any<boost::type_erasure::any<C, T>> = true;

struct type_erased_rtti : policies::rtti {
  template <class Class> static constexpr auto is_polymorphic = is_any<Class>;

  template <typename T> static type_id static_type() {
    if constexpr (is_any<T>) {
      return reinterpret_cast<type_id>(&typeid(void));
    } else {
      return reinterpret_cast<type_id>(&typeid(T));
    }
  }

  template <typename T> static type_id dynamic_type(const T &obj) {
    return reinterpret_cast<type_id>(&boost::type_erasure::typeid_of(obj));
  }

  template <class Stream> static void type_name(type_id type, Stream &stream) {
    stream << reinterpret_cast<const std::type_info *>(type)->name();
  }

  static std::type_index type_index(type_id type) {
    return std::type_index(*reinterpret_cast<const std::type_info *>(type));
  }

  template <typename D, typename B> static D dynamic_cast_ref(B &&obj) {
    // cast through void* for a fast, unchecked cast
    using unref = std::remove_reference_t<D>;
    if constexpr (std::is_const_v<unref>) {
      return *static_cast<unref *>(
          boost::type_erasure::any_cast<const void *>(&obj));
    } else {
      return *static_cast<unref *>(boost::type_erasure::any_cast<void *>(&obj));
    }
  }
};

struct type_erased_policy
    : boost::openmethod::policies::debug::fork<type_erased_policy>::replace<
          boost::openmethod::policies::rtti, type_erased_rtti> {};

BOOST_OPENMETHOD_CLASSES(void, type_erased_policy)

template <typename Policy, typename T, typename... Bases>
boost::openmethod::detail::class_declaration_aux<
    Policy, boost::mp11::mp_list<T, Bases...>>
    global_register;

template <typename T, typename Policy> struct openmethod_vptr {
  static boost::openmethod::vptr_type apply(const T &) {
    const auto &_ = global_register<Policy, T, void>;
    return Policy::template static_vptr<T>;
  }
};

namespace boost::type_erasure {
template <typename T, typename Policy, typename Base>
struct concept_interface<::openmethod_vptr<T, Policy>, Base, T> : Base {
  friend boost::openmethod::vptr_type boost_openmethod_vptr(
      const typename boost::type_erasure::derived<Base>::type &arg) {
    return boost::type_erasure::call(::openmethod_vptr<T, Policy>(), arg);
  }
};
} // namespace boost::type_erasure

template <typename T = boost::type_erasure::_self,
          typename Policy = type_erased_policy>
using openmethod =
    boost::mp11::mp_list<boost::type_erasure::typeid_<>,
                         openmethod_vptr<boost::type_erasure::_self, Policy>>;

using Base = boost::type_erasure::any<boost::mp11::mp_list<
    openmethod<>, boost::type_erasure::copy_constructible<>>>;
using BaseRef =
    boost::type_erasure::any<openmethod<>, boost::type_erasure::_self &>;

BOOST_OPENMETHOD(foo, (virtual_<const BaseRef &>), void, type_erased_policy)

BOOST_OPENMETHOD_OVERRIDE(foo, (int &i), void) { i = 5; }

BOOST_OPENMETHOD_OVERRIDE(foo, (double &d), void) { d = 2.718; }

int main() {
  boost::openmethod::initialize<type_erased_policy>();
  int i = 0;
  double d = 0;
  BaseRef b1(i);
  BaseRef b2(d);
  foo(b1);
  foo(b2);
  std::cout << i << std::endl;
  std::cout << d << std::endl;
  Base b3(42);
  foo(b3);
  std::cout << any_cast<int>(b3) << std::endl;
}