Question

I have an interface like this:

public interface IUser{
    //some properties here

    T ToDerived(User u);
}

I’m new to interface development, so here’s what I’m trying to accomplish. I will have a base class

public class User 

that does NOT implement the above interface. Then I will have a derived class

SalesUser : User, IUser
{
    //no properties needed because they exist in the User class

    SalesUser ToDerived(User u)
    {
        //code for converting a base User to a derived SalesUser
    }
}

I would like to write the function for ToDerived(User u) in the SalesUser class, but in the interface, I do not know how to define this as the ToDerived method declaration that I have now in the interface is not compiling.

I hope this makes sense.

Answer 1

public interface IUser<T> where T : User
{
    //some properties here

    T ToDerived(User u);
}

SalesUser : User, IUser<SalesUser>
{
    //no properties needed because they exist in the User class

    SalesUser ToDerived(User u)
    {
        //code for converting a base User to a derived SalesUser
    }
}

Not sure this is what you want, but I added a generic type constraint on the interface to ensure that the generic type is User or inherits from it.