using System;

public class Program

{

    public static void Main()

    {

        var bird = new Duck() { DuckyProperty = "23" } as IBird; //the cast is necessary to simulate a real world scenario

        var factory = new BirdProcessorFactory();

        var provider = factory.GetBirdProcessor(bird);

​

        var weight = provider.GetBirdWeight(bird);

        Console.WriteLine(weight);

    }

}

​

public interface IBird

{

​

}

​

public class Duck : IBird

{

    public string DuckyProperty { get; set; } //this property is Duck specific!

}

​

public interface IBirdProcessor<in T> where T : IBird

{

    double GetBirdWeight(T obj); //this does not compile

}

​

public class DuckProcessor : IBirdProcessor<Duck>

{

    public double GetBirdWeight(Duck duck)

    {

        return double.Parse(duck.DuckyProperty);

    }

}

​

public class BirdProcessorFactory

{

    public IBirdProcessor<T> GetBirdProcessor<T>(T obj) where T : IBird

    {

        return (IBirdProcessor<T>)new DuckProcessor();

    }

}