using System;

public interface IProduct

{

  void SayHello();

}

​

public class ProductA: IProduct

{

  public void SayHello()

  {

    Console.WriteLine("Hello, I'm ProductA");

  }

}

​

public class ProductB: IProduct

{

  public void SayHello()

  {

    Console.WriteLine("Hello, I'm ProductB");

  }

}

​

​

public class A

{

  public IProduct DoSomething(IProduct product)

  {

    product.SayHello();

    return product;

  }

}

​

public class B<T> where T: IProduct

{

  public T DoSomething(T product)

  {

    product.SayHello();

    return product;

  }

}

​

public class Program

{

    public static void Main()

    {

      var productA = new ProductA();

      var productB = new ProductB();

      var a = new A();

      a.DoSomething(productA);

      a.DoSomething(productB);

      var b = new B<ProductA>();

      b.DoSomething(productA);

      var c = new B<ProductB>();

      c.DoSomething(productB);

    }

}

​