feat(reflection): impl nullable trait

core/CMakeLists.txt

@@ -39,6 +39,7 @@ set(CUBOS_CORE_SOURCE
     "src/cubos/core/reflection/traits/array.cpp"
     "src/cubos/core/reflection/traits/dictionary.cpp"
     "src/cubos/core/reflection/traits/string_conversion.cpp"
+    "src/cubos/core/reflection/traits/nullable.cpp"
     "src/cubos/core/reflection/external/primitives.cpp"
     "src/cubos/core/reflection/external/string.cpp"
     "src/cubos/core/reflection/external/uuid.cpp"

core/include/cubos/core/reflection/traits/nullable.hpp

@@ -0,0 +1,41 @@
+/// @file
+/// @brief Class @ref cubos::core::reflection::NullableTrait.
+/// @ingroup core-reflection
+
+#pragma once
+
+#include <cubos/core/reflection/reflect.hpp>
+
+namespace cubos::core::reflection
+{
+    /// @brief Used to manipulate values of null-representable types.
+    /// @see See @ref examples-core-reflection-traits-nullable for an example of using this trait.
+    /// @ingroup core-reflection
+    class NullableTrait
+    {
+    public:
+        /// @brief Function pointer to check if a value represents null.
+        using IsNull = bool (*)(const void* instance);
+
+        /// @brief Function pointer to set a value to its null representation.
+        using SetToNull = void (*)(void* instance);
+
+        /// @brief Constructs.
+        /// @param into IsNull.
+        /// @param from SetToNull.
+        NullableTrait(IsNull isNull, SetToNull setToNull);
+
+        /// @brief Checks if the given value represents null.
+        /// @param instance Instance.
+        /// @return Whether the value represents null.
+        bool isNull(const void* instance) const;
+
+        /// @brief Sets a value to its null representation.
+        /// @param instance Instance.
+        void setToNull(void* instance) const;
+
+    private:
+        IsNull mIsNull;
+        SetToNull mSetToNull;
+    };
+} // namespace cubos::core::reflection

core/src/cubos/core/reflection/traits/nullable.cpp

@@ -0,0 +1,19 @@
+#include <cubos/core/reflection/traits/nullable.hpp>
+
+using cubos::core::reflection::NullableTrait;
+
+NullableTrait::NullableTrait(IsNull isNull, SetToNull setToNull)
+    : mIsNull(isNull)
+    , mSetToNull(setToNull)
+{
+}
+
+bool NullableTrait::isNull(const void* instance) const
+{
+    return mIsNull(instance);
+}
+
+void NullableTrait::setToNull(void* instance) const
+{
+    mSetToNull(instance);
+}