public abstract class Shape { }
public class Circle: Shape { }

public interface IContainer<T>
{
    T Figure { get; set; }
}

public class Container<T> : IContainer<T>
{
    public T Figure { get; set; }

    public Container(T figure)
    {
        this.Figure = figure;
    }
}

class Program
{
    static void Main(string[] args)
    {
        Circle circle = new Circle();
        IContainer<Circle> container = new Container<Circle>(circle);
        Console.WriteLine(container.Figure.ToString());
    }
}