From bd98e6ec9eebcb5025bb1f79b3dacf7624f9fdbb Mon Sep 17 00:00:00 2001
From: tyanmahou <tyanmahou@gmail.com>
Date: Sun, 12 Nov 2023 23:18:04 +0900
Subject: [PATCH] add variant_ptr

---
 Re-Abyss/app/utils/Memory/variant_ptr.hpp | 97 +++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 Re-Abyss/app/utils/Memory/variant_ptr.hpp

diff --git a/Re-Abyss/app/utils/Memory/variant_ptr.hpp b/Re-Abyss/app/utils/Memory/variant_ptr.hpp
new file mode 100644
index 00000000..acbd8468
--- /dev/null
+++ b/Re-Abyss/app/utils/Memory/variant_ptr.hpp
@@ -0,0 +1,97 @@
+#include <type_traits>
+#include <concepts>
+#include <variant>
+
+namespace abyss
+{
+    template<class Base, std::derived_from<Base>... Deriveds>
+    class variant_ptr
+    {
+    public:
+        variant_ptr() noexcept = default;
+        template<class Type> requires std::same_as<Type, Base> || (std::same_as<Type, Deriveds> || ...)
+            variant_ptr(Type * ptr) noexcept
+        {
+            if (ptr == nullptr) {
+                return;
+            }
+            const auto& rtti = typeid(*ptr);
+            if (rtti == typeid(Type)) [[likely]] {
+                m_ptr = ptr;
+                return;
+                }
+            Base* base = static_cast<Base*>(ptr);
+            if (rtti == typeid(Base)) {
+                m_ptr = base;
+                return;
+            }
+            auto derived_checks = [&]<class T>(T*) {
+                if (rtti == typeid(T)) {
+                    if constexpr (std::convertible_to<Base*, T*>) {
+                        m_ptr = static_cast<T*>(base);
+                        return true;
+                    } else {
+                        m_ptr = dynamic_cast<T*>(base);
+                        return true;
+                    }
+                }
+                return false;
+            };
+            if ((derived_checks(static_cast<Deriveds*>(nullptr)) || ...)) {
+                return;
+            }
+            m_ptr = ptr;
+        }
+        variant_ptr(const variant_ptr& other) noexcept :
+            m_ptr(other.m_ptr)
+        {}
+        variant_ptr(variant_ptr&& other) noexcept :
+            m_ptr(std::move(other.m_ptr))
+        {}
+        variant_ptr(std::nullptr_t) noexcept :
+            m_ptr()
+        {}
+        Base* get() const noexcept
+        {
+            return cast_to<Base*>();
+        }
+        Base* operator ->() const noexcept
+        {
+            return get();
+        }
+        Base& operator *() const noexcept
+        {
+            return *get();
+        }
+        template<class ToPtr> requires std::is_pointer_v<ToPtr> && (std::convertible_to<Base*, ToPtr> || (std::convertible_to<Deriveds*, ToPtr> || ...))
+            ToPtr cast_to() const noexcept
+        {
+            return std::visit([]<class T>(T * ptr)->ToPtr {
+                if constexpr (std::convertible_to<T*, ToPtr>) {
+                    return static_cast<ToPtr>(ptr);
+                } else {
+                    return nullptr;
+                }
+            }, m_ptr);
+        }
+        explicit operator bool() const noexcept
+        {
+            return get() != nullptr;
+        }
+    private:
+        std::variant<Base*, Deriveds*...> m_ptr;
+    };
+    template<class ToPtr>
+    struct variant_dynamic_cast_impl
+    {
+        template<class Base, std::derived_from<Base>... Deriveds>
+            requires std::is_pointer_v<ToPtr> && (std::convertible_to<Base*, ToPtr> || (std::convertible_to<Deriveds*, ToPtr> || ...))
+        ToPtr operator()(const variant_ptr<Base, Deriveds...>& ptr) const noexcept
+        {
+            return ptr.template cast_to<ToPtr>();
+        }
+    };
+
+    template<class ToPtr>
+    inline constexpr auto variant_dynamic_cast = variant_dynamic_cast_impl<ToPtr>{};
+}