add is_virtual_base_of trait

headers/meta.hpp/meta_base.hpp

@@ -19,6 +19,7 @@
 #include "meta_base/insert_or_assign.hpp"
 #include "meta_base/intrusive_ptr.hpp"
 #include "meta_base/is_in_place_type.hpp"
+#include "meta_base/is_virtual_base_of.hpp"
 #include "meta_base/memory_buffer.hpp"
 #include "meta_base/noncopyable.hpp"
 #include "meta_base/nonesuch.hpp"

headers/meta.hpp/meta_base/is_virtual_base_of.hpp

@@ -0,0 +1,41 @@
+/*******************************************************************************
+ * This file is part of the "https://github.com/blackmatov/meta.hpp"
+ * For conditions of distribution and use, see copyright notice in LICENSE.md
+ * Copyright (C) 2021-2023, by Matvey Cherevko (blackmatov@gmail.com)
+ ******************************************************************************/
+
+#pragma once
+
+#include "base.hpp"
+
+namespace meta_hpp::detail
+{
+    namespace impl
+    {
+        template < typename From, typename To >
+        constexpr bool is_virtual_base_of_impl(...) noexcept {
+            return false;
+        }
+
+        template <
+            typename From,
+            typename To,
+            decltype(static_cast<const volatile To*>(std::declval<const volatile From*>())) = nullptr >
+        constexpr bool is_virtual_base_of_impl(int) noexcept {
+            return true;
+        }
+    }
+
+    // clang-format off
+
+    template < typename Base, typename Derived >
+    struct is_virtual_base_of : std::integral_constant<bool,
+          std::is_base_of_v<Base, Derived> &&
+          impl::is_virtual_base_of_impl<Derived, Base>(0) &&
+          !impl::is_virtual_base_of_impl<Base, Derived>(0)> {};
+
+    // clang-format on
+
+    template < typename Base, typename Derived >
+    inline constexpr bool is_virtual_base_of_v = is_virtual_base_of<Base, Derived>::value;
+}