How to use common method for example AddUser with domain objects OldVersionProject.User and NewVersionProject.User

Question

I mean that I have two objects for which number of variables and names completely the same with only 1 difference that they are stored in two different assemblies.

Is it possible to mark somehow the dll that it is the same objects, so I could use "User" object from the old project and "User" from the new project with the same common service AddUser

Answer 1

This is screaming out for an interface

namespace OldVersionProject
{
    public class User : IUser
    {
    }
}

namespace NewVersionProject
{
    public class User : IUser
    {
    }
}

public interface IUser
{
    // common properties
}

Then in your common service

public void AddUser(IUser user)
{
    // user is now version independant
}

Answer 2

Extract the User class into a shared library, say, BusinessObjects, and reference that library from all projects that need a User class.