Liskov Substitution Principle

  • Subtypes must be substitutable for their base types.
  • Minimize null checks with c# features,guard clauses, null object design pattern 
  • Follow lsp and make sure to fully implement interfaces
				
					namespace LiskovSubsPrinciple
{
    public class Square : Rectangle
    {
        private int _height;
        private int _width;
        public override int Height
        {
            get { return _height; }
            set
            {
                _width = value;
                _height = value;
            }
        }
        public override int Width
        {
            get { return _width; }
            set
            {
                _width = value;
                _height = value;
            }
        }
    }

    public class AreaCalculator
    {
        public static int CalculateArea(Rectangle r)
        {
            return r.Height * r.Width;
        }
    }

    public class Rectangle
    {
        public virtual int Height { get; set; }
        public virtual int Width { get; set; }
    }
}

				
			
				
					using LiskovSubsPrinciple;

Rectangle newRectangle = new Square();
newRectangle.Height = 4;
newRectangle.Width = 6;
Console.WriteLine(AreaCalculator.CalculateArea(newRectangle));//36

36

				
					namespace LiskovSubsPrinciple
{
    
    public class AreaCalculator
    {
        public static int CalculateArea(Rectangle r)
        {
            return r.Height * r.Width;
        }

        public static int CalculateSquareArea(Rectangle r)
        {
            return r.Height * r.Height;
        }
    }

    public class Rectangle
    {
        public virtual int Height { get; set; }
        public virtual int Width { get; set; }
        public bool IsSquare => Height == Width;
    }
}

				
			
				
					using LiskovSubsPrinciple;

Rectangle newRectangle = new ();
newRectangle.Height = 4;
newRectangle.Width = 6;
if (newRectangle.IsSquare)
{
    Console.WriteLine("this is a square");
    Console.WriteLine(AreaCalculator.CalculateSquareArea(newRectangle));
}
else
{
    Console.WriteLine("this is a rectangle");
    Console.WriteLine(AreaCalculator.CalculateArea(newRectangle));
}


				
			
				
					public class Rectangle
    {
        public virtual int Height { get; set; }
        public virtual int Width { get; set; }
    }

    public class Square
    {
        public virtual int Side { get; set; }
    }

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