using System;

using System.Linq;

​

public interface IEntity 

{

    string Firstname { get; }

}

​

public interface IModel 

{

    string Surname { get; }

}

​

public class EntityA : IEntity

{

    public string Firstname 

    {

        get

        {

            return "Ryan";

        }

    }

}

​

public class EntityB : IEntity

{

    public string Firstname 

    {

        get

        {

            return "Winter";

        }

    }

}

​

public class ModelA : IModel 

{

    public string Surname 

    {

        get

        {

            return "Wallace";

        }

    }

}

​

public class ModelB : IModel 

{

    public string Surname 

    {

        get

        {

            return "The Best";

        }

    }

}

​

public class Program

{

    public static string Foo<E, M>(E entity, M model) 

        where E : IEntity 

        where M : IModel    

    {

        return "BASE Error";

    }

    public static string Foo(EntityA entity, ModelA model) 

    {

        return string.Format("Method 1 : {0} {1}", entity.Firstname, model.Surname );

    }

    public static string Foo(EntityB entity, ModelA model) 

    {

        return string.Format("Method 2 : {0} {1}", entity.Firstname, model.Surname );

    }

    public static string Foo(EntityA entity, ModelB model) 

    {

        return string.Format("Method 3 : {0} {1}", entity.Firstname, model.Surname );

    }

    public static string Foo(EntityB entity, ModelB model) 

    {

        return string.Format("Method 4 : {0} {1}", entity.Firstname, model.Surname );

    }

​

    public static void Main()

    {       

        var ea = new EntityA();

        var eb = new EntityB();

        var ma = new ModelA();

        var mb = new ModelB();

        Console.WriteLine( Foo(ea, ma) );

        Console.WriteLine( Foo(eb, ma) );

        Console.WriteLine( Foo(ea, mb) );

        Console.WriteLine( Foo(eb, mb) );

    }

}