// Based on stackoverflow comment:

// https://softwareengineering.stackexchange.com/a/352269/277090

public class Program

{

    public static void Main()

    {

        var state = new MyState();

        state = DoSomething(state);

    }

    // Function can use MyString and MyInt of state, but not MyDouble.

    public static T DoSomething<T>(T state) where T : IHasMyString, IHasMyInt

    {

        var s = state.GetMyString();

        var i = state.GetMyInt();

        return state;

    }

}

​

public interface IHasMyInt

{

    int GetMyInt();

}

​

public interface IHasMyString

{

    string GetMyString();

}

​

public interface IHasMyDouble

{

    string GetMyDouble();

}

​

public class MyState : IHasMyInt, IHasMyString

{

    public int MyInt {get; set; }

    public string MyString {get; set; }

    public double MyDouble {get; set; }

​

    public int GetMyInt () 

    {

        return MyInt;

    }

​

    public string GetMyString ()

    {

        return MyString;

    }

​

    public double GetMyDouble ()

    {

        return MyDouble;

    }

}

​