c++ - 前向声明 boost.type_erasure 引用类型

Question

我在我的代码库中使用 boost.type_erasure。到目前为止的经验，考虑到它的功能，效果非常好。

我希望能够为我的 API 转发声明一个“类型删除的引用类型”。这在 using 和 typedef 之外留下了，因为它们不允许前向声明。

对于值类型，一切都很好:

class any_game_state : public
boost::type_erasure::any<
boost::mpl::vector<has_enter<void ()>,
                   has_update<bool (std::chrono::milliseconds)>,
                   has_exit<int ()>,
                   has_get_resolution<std::pair<int, int> (),
                                      const
                                      boost::type_erasure::_self>,
                   has_get_position<std::pair<int, int> (),
                                    const
                                    boost::type_erasure::_self>,
                   has_get_scene_root<boost::any (), const
                                      boost::type_erasure::_self>,
                   boost::type_erasure::copy_constructible<>,
                   boost::type_erasure::relaxed>> {
    using base = boost::type_erasure::any<...identical_contents>;

    using base::base;
};

但是当我尝试对其相应的引用执行相同操作时，它不起作用:

class any_game_state_ref : public
boost::type_erasure::any<
boost::mpl::vector<has_enter<void ()>,
                   has_update<bool (std::chrono::milliseconds)>,
                   has_exit<int ()>,
                   has_get_resolution<std::pair<int, int> (),
                                      const
                                      boost::type_erasure::_self>,
                   has_get_position<std::pair<int, int> (),
                                    const
                                    boost::type_erasure::_self>,
                   has_get_scene_root<boost::any (), const
                                      boost::type_erasure::_self>,
                   boost::type_erasure::copy_constructible<>,
                   boost::type_erasure::relaxed>,
                   boost::type_erasure::_self&> {
    using base = boost::type_erasure::any<...identical_contents>;

    using base::base;
};

如果我使用 using 作为“引用类型”一切正常，但我失去了转发声明引用类型的能力。

我得到的错误如下:

在 src/barvie/controller/game_action_state.cpp 包含的文件中:3:在/usr/local/include/boost/type_erasure/any_cast.hpp:24 包含的文件中:/usr/local/include/boost/type_erasure/any.hpp:1290:12: 错误:'boost::disable_if, has_update >), boost::type_erasure::_self>, has_exit, has_get_resolution 中没有名为'type'的类型(), const boost::type_erasure::_self>, has_get_position (), const boost::type_erasure::_self>, has_get_scene_root, boost::type_erasure::copy_constructible, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, boost::mpl::vector, has_update >), boost::type_erasure::_self>, has_exit, has_get_resolution (), const boost::type_erasure::_self>, has_get_position (), const boost: :type_erasure::_self>, has_get_scene_root, boost::type_erasure::copy_constructible, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>>, boost::is_const, mpl_::bool_, mpl_::bool_, mpl_::bool_ >, void>'

::type* = 0 ~~~^~~~ ../libbarvie/src/barvie/controller/any_game_state.hpp:95:17: note: in instantiation of member function 'boost::type_erasure::any, has_update >), boost::type_erasure::_self>, has_exit, has_get_resolution (), const boost::type_erasure::_self>, has_get_position (), const boost::type_erasure::_self>, has_get_scene_root, boost::type_erasure::copy_constructible, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, boost::type_erasure::_self &>::any' requested here using base::base; ^ src/barvie/controller/game_action_state.cpp:291:18: note: while substituting deduced template arguments into function template 'any_game_state_ref' [with Concept2 = boost::mpl::vector, has_update >), boost::type_erasure::_self>, has_exit, has_get_resolution (), const boost::type_erasure::_self>, has_get_position (), const boost::type_erasure::_self>, has_get_scene_root, boost::type_erasure::copy_constructible, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, Tag2 = boost::type_erasure::_self] (this, ^ In file included from src/barvie/controller/game_action_state.cpp:3: In file included from /usr/local/include/boost/type_erasure/any_cast.hpp:24: /usr/local/include/boost/type_erasure/any.hpp:1323:12: error: no type named 'type' in 'boost::disable_if, has_update >), boost::type_erasure::_self>, has_exit, has_get_resolution (), const boost::type_erasure::_self>, has_get_position (), const boost::type_erasure::_self>, has_get_scene_root, boost::type_erasure::copy_constructible, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, boost::mpl::vector, has_update >), boost::type_erasure::_self>, has_exit, has_get_resolution (), const boost::type_erasure::_self>, has_get_position (), const boost::type_erasure::_self>, has_get_scene_root, boost::type_erasure::copy_constructible, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na> >, boost::is_const, mpl_::bool_, mpl_::bool_, mpl_::bool_ >, void>' ::type = 0 ~~~^~~~ ../libbarvie/src/barvie/controller/any_game_state.hpp:95:17: note: in instantiation of member function 'boost::type_erasure::any, has_update >), boost::type_erasure::_self>, has_exit, has_get_resolution (), const boost::type_erasure::_self>, has_get_position (), const boost::type_erasure::_self>, has_get_scene_root, boost::type_erasure::copy_constructible, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, boost::type_erasure::_self &>::any' requested here using base::base; ^ src/barvie/controller/game_action_state.cpp:291:18: note: while substituting deduced template arguments into function template 'any_game_state_ref' [with Concept2 = boost::mpl::vector, has_update >), boost::type_erasure::_self>, has_exit, has_get_resolution (), const boost::type_erasure::_self>, has_get_position (), const boost::type_erasure::_self>, has_get_scene_root, boost::type_erasure::copy_constructible, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, Tag2 = boost::type_erasure::_self &] (*this,

Answer 1

我找到了一个解决方案。解决方案是放弃引用类型的继承构造函数，而不是我使用等效的手动继承构造函数的继承构造函数。似乎与继承的构造函数混合的模板的某些东西不能很好地发挥作用:

template <class...Args>
any_game_state_ref(Args &&... args) : base(std::forward<Args>(args)...)
{}

这成功了，现在我也可以转发声明类型删除的引用了。