Native C++ callback with inherited structs

From C# I need to setup a callback to C++ where the data received with the callback originates from structs with inheritance (See the distilled code below in the C++ section).

I believe the structs in C++ are collapsed by the compiler because they do not contain any virtual functions? So using the collapsed data class 'CollapsedCallbackInfo' in C# actually works for that specific data class. But having a lot of different data classes with multiple layers of inheritence in the real problem, is there a way solve this challenge? I need some common type to use in my delegate definition.

C#

Callback setup

[DllImport("NativeDLL", CallingConvention = CallingConvention.Cdecl)] public static extern void SetupCallback(CallbackFunc callback);

[UnmanagedFunctionPointer(CallingConvention.Cdecl)] public delegate void CallbackFunc(BaseCallbackInfo baseCallbackInfo);

C# Data classes

[StructLayout(LayoutKind.Sequential)] public class BaseCallbackInfo { public uint base_data; };

[StructLayout(LayoutKind.Sequential)] public class ConcreteCallbackInfo : BaseCallbackInfo { public uint concrete_data; };


Collapsed data class

[StructLayout(LayoutKind.Sequential)]
public class CollapsedCallbackInfo 
{
    public uint base_data;
    public uint concrete_data;
};

Test Class that illustrates the callback setup

public class TestClass { public void RegisterCallback() { SetupCallback(new CallbackFunc(OnCallback)); }

public void OnCallback(BaseCallbackInfo baseCallbackInfo) { // In the real problem I know this cast is valid ConcreteCallbackInfo ccbi = baseCallbackInfo as ConcreteCallbackInfo; Debug.Log(ccbi.concrete_data) }

}

C++

Data classes

struct BaseCallbackInfo { uint base_data; };

struct ConcreteCallbackInfo : public BaseCallbackInfo { uint concrete_data; };

C-style Callback definition and external interface

typedef void( *CallbackFunc )( BaseCallbackInfo* in_pCallbackInfo );

extern "C" __declspec(dllexport) void SetupCallback(CallbackFunc callback);