//function i want to call
public static void GuiDelegate(string message)
{
    WriteToWPFGui(message);
}

//notice i need to marshall my string from unmanaged <-> managed, my pinvoke sig
public delegate void CppCallback([MarshalAs(UnmanagedType.LPWStr)] string message);

public static void GuiWriter(CppCallback c)
{
    GuiWriter(c);
}

//we need to access C++
[DllImport("C:\projectName.dll", EntryPoint="CSharp_GuiWriter")] via a dll
public static extern void GuiWriter(CppCallback jarg1);

//CppCallback is defined above
public static CppCallback gui_functor;

delegate void StringDelegate(string message);

//delegate assignment
StringDelegate gui_callback = GuiDelegate;
gui_functor = new CppCallback(gui_callback);

//this points to pinvoke sig -> pinvoke will step into
projName.GuiWriter(gui_functor);

#pragma once
#include <windows.h>
#include <tchar.h>

namespace lib2 {

    typedef void (__stdcall *Callback)(PCWSTR);
    static Callback gui;

    public class Class1
    {
        void makeCSHarpPrintThisText()
        {
            (*gui)(_T("make C# print this text"));
        }
    };


    __declspec(dllexport) void __stdcall CSharp_GuiWriter(void * jarg1)
    {
        Callback arg1 = (Callback) 0 ;
        arg1 = (Callback)jarg1;
        gui = arg1;
    }
}