using System;

public class Program

{

    public static void Main()

    {

        var square = new Square() { Area = 4.0, SideLength = 2 };

        var shape = new Shape() { Area = 3.0 };

        //Generic way

        var genericHandler = new ShapeHandlerGeneric<Shape>(square);        

        Console.WriteLine(genericHandler.GetArea());

        //Non generic way

        LogArea(square);

        LogArea(shape);

    }

    public static void LogArea(Shape shape)

    {

        Console.WriteLine(shape.Area);

    }

}

​

public class Shape

{

    public double Area { get; set; }

}

​

public class Square : Shape

{

    public int SideLength { get; set; }

    // more stuff

}

​

//Using generics

public class ShapeHandlerGeneric<T> where T:Shape

{   

    public ShapeHandlerGeneric(T shape)

    {

        MyShape = shape;

    }

    private T MyShape;

    public double GetArea()

    {

        return MyShape.Area;

    }

}