Boost C++ Libraries

boost/type_index/runtime_cast/register_runtime_class.hpp

//
// Copyright (c) Chris Glover, 2016.
//
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

#ifndef BOOST_TYPE_INDEX_RUNTIME_CAST_REGISTER_RUNTIME_CLASS_HPP
#define BOOST_TYPE_INDEX_RUNTIME_CAST_REGISTER_RUNTIME_CLASS_HPP

/// \file register_runtime_class.hpp
/// \brief Contains the macros BOOST_TYPE_INDEX_IMPLEMENT_RUNTIME_CAST and
/// BOOST_TYPE_INDEX_REGISTER_RUNTIME_CLASS
#include <boost/type_index.hpp>
#include <boost/preprocessor/seq/for_each.hpp>

#ifdef BOOST_HAS_PRAGMA_ONCE
# pragma once
#endif

namespace boost { namespace typeindex {

namespace detail {

template<typename T>
inline type_index runtime_class_construct_type_id(T const*) {
    return type_id<T>();
}

} // namespace detail

}} // namespace boost::typeindex

/// @cond

#define BOOST_TYPE_INDEX_CHECK_BASE_(r, data, Base) \
    if(void const* ret_val = this->Base::boost_type_index_find_instance_(idx)) return ret_val;

/// @endcond

/// \def BOOST_TYPE_INDEX_REGISTER_RUNTIME_CLASS
/// \brief Macro used to make a class compatible with boost::typeindex::runtime_cast
///
/// BOOST_TYPE_INDEX_REGISTER_RUNTIME_CLASS generates a virtual function
/// in the current class that, when combined with the supplied base class information, allows
/// boost::typeindex::runtime_cast to accurately convert between dynamic types of instances of
/// the current class.
///
/// BOOST_TYPE_INDEX_REGISTER_RUNTIME_CLASS also adds support for boost::typeindex::type_id_runtime
/// by including BOOST_TYPE_INDEX_REGISTER_CLASS. It is typical that these features are used together,
/// but in the event that BOOST_TYPE_INDEX_REGISTER_CLASS is undesirable in the current class,
/// BOOST_TYPE_INDEX_IMPLEMENT_RUNTIME_CAST is provided.
///
/// \b Example:
/// \code
/// struct base1 {
///     BOOST_TYPE_INDEX_REGISTER_RUNTIME_CLASS(BOOST_TYPE_INDEX_NO_BASE_CLASS)
///     virtual ~base1();
/// };
///
/// struct base2 {
///     BOOST_TYPE_INDEX_REGISTER_RUNTIME_CLASS(BOOST_TYPE_INDEX_NO_BASE_CLASS)
///     virtual ~base2();
/// };
///
/// struct derived1 : base1 {
///     BOOST_TYPE_INDEX_REGISTER_RUNTIME_CLASS((base1))
/// };
///
/// struct derived2 : base1, base2 {
///     BOOST_TYPE_INDEX_REGISTER_RUNTIME_CLASS((base1)(base2))
/// };
///
/// ...
///
/// base1* pb1 = get_object();
/// if(derived2* pb2 = boost::typeindex::runtime_cast<derived2*>(pb1)) {
///     assert(boost::typeindex::type_id_runtime(*pb1)) == boost::typeindex::type_id<derived2>());
/// }
/// \endcode
///
/// \param base_class_seq A Boost.Preprocessor sequence of the current class' direct bases, or
/// BOOST_TYPE_INDEX_NO_BASE_CLASS if this class has no direct base classes.
#define BOOST_TYPE_INDEX_REGISTER_RUNTIME_CLASS(base_class_seq)                                                          \
    BOOST_TYPE_INDEX_REGISTER_CLASS                                                                                      \
    BOOST_TYPE_INDEX_IMPLEMENT_RUNTIME_CAST(base_class_seq)

/// \def BOOST_TYPE_INDEX_IMPLEMENT_RUNTIME_CAST
/// \brief Macro used to make a class compatible with boost::typeindex::runtime_cast without including
/// support for boost::typeindex::type_id_runtime.
///
/// BOOST_TYPE_INDEX_IMPLEMENT_RUNTIME_CAST is provided as an alternative to BOOST_TYPE_INDEX_REGISTER_RUNTIME_CLASS
/// in the event that support for boost::typeindex::type_id_runtime is undesirable.
///
/// \b Example:
/// \code
/// struct base1 {
///     BOOST_TYPE_INDEX_IMPLEMENT_RUNTIME_CAST(BOOST_TYPE_INDEX_NO_BASE_CLASS)
///     virtual ~base1();
/// };
///
/// struct base2 {
///     BOOST_TYPE_INDEX_IMPLEMENT_RUNTIME_CAST(BOOST_TYPE_INDEX_NO_BASE_CLASS)
///     virtual ~base2();
/// };
///
/// struct derived1 : base1 {
///     BOOST_TYPE_INDEX_IMPLEMENT_RUNTIME_CAST((base1))
/// };
///
/// struct derived2 : base1, base2 {
///     BOOST_TYPE_INDEX_IMPLEMENT_RUNTIME_CAST((base1)(base2))
/// };
///
/// ...
///
/// base1* pb1 = get_object();
/// if(derived2* pb2 = boost::typeindex::runtime_cast<derived2*>(pb1))
/// { /* can't call boost::typeindex::type_id_runtime(*pb1) here */ }
/// \endcode
///
/// \param base_class_seq A Boost.Preprocessor sequence of the current class' direct bases, or
/// BOOST_TYPE_INDEX_NO_BASE_CLASS if this class has no direct base classes.
#define BOOST_TYPE_INDEX_IMPLEMENT_RUNTIME_CAST(base_class_seq)                                                          \
    virtual void const* boost_type_index_find_instance_(boost::typeindex::type_index const& idx) const BOOST_NOEXCEPT {  \
        if(idx == boost::typeindex::detail::runtime_class_construct_type_id(this))                                       \
            return this;                                                                                                 \
         BOOST_PP_SEQ_FOR_EACH(BOOST_TYPE_INDEX_CHECK_BASE_, _, base_class_seq)                                          \
         return NULL;                                                                                                    \
    }

/// \def BOOST_TYPE_INDEX_NO_BASE_CLASS
/// \brief Instructs BOOST_TYPE_INDEX_REGISTER_RUNTIME_CLASS and BOOST_TYPE_INDEX_IMPLEMENT_RUNTIME_CAST
/// that this class has no base classes.
#define BOOST_TYPE_INDEX_NO_BASE_CLASS BOOST_PP_SEQ_NIL

#endif // BOOST_TYPE_INDEX_RUNTIME_CAST_REGISTER_RUNTIME_CLASS_HPP