Simple C++/C# interop with a method returning a structure

Program.cs

using System;
using System.Runtime.InteropServices;

namespace Executable
{
    struct SimpleStruct
    {
        public SimpleStruct(int value)
        {
            Value = value;
        }

        public int Value;
    }

    class Program
    {
        [DllImport("Library.dll")]
        static extern void InstallCallback([MarshalAs(UnmanagedType.FunctionPtr)]MyCallback callback);
        [DllImport("Library.dll")]
        static extern void FireCallback(int x, int y);

        delegate SimpleStruct MyCallback(int x, int y);

        static SimpleStruct MakeResult(int x, int y)
        {
            return new SimpleStruct(x + y);
        }

        static void Main(string[] args)
        {
            InstallCallback(new MyCallback(MakeResult));
            Console.WriteLine("Firing callback!");
            FireCallback(1, 2);
        }
    }
}