Skip to main content

SOLID (3/5) - Liskov substitution principle

  SOLID (3/5) - Liskov substitution principle


Substitutability is a principle in object-oriented programming stating that, in a computer program, if S is a subtype of T, then objects of type T may be replaced with objects of type S (i.e., an object of type T may be substituted with any object of a subtype S) without altering any of the desirable properties of the program (correctness, task performed, etc.). More formally, the Liskov substitution principle (LSP) is a particular definition of a subtyping relation, called (strong) behavioral subtyping. It is a semantic rather than merely syntactic relation, because it intends to guarantee semantic interoperability of types in a hierarchy, object types in particular.

using System;

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

        public Rectangle()
        {

        }

        public Rectangle(int width, int height)
        {
            this.Width = width;
            this.Height = height;
        }

        public override string ToString()
        {
            return $"{nameof(Width)}: {Width}, {nameof(Height)}: {Height}";
        }
    }

    public class Square : Rectangle 
    {
        //public new int Width
        public override int Width
        { 
            set { base.Width = base.Height = value; } 
        }
        //public new int Height
        public override int Height
        { 
            set { base.Width = base.Height = value; } 
        }
    }

    class Program
    {
        public static int Area(Rectangle r) => r.Height * r.Width;

        static void Main(string[] args)
        {
            Rectangle r = new Rectangle(2,3);
            Console.WriteLine($"{r} as area {Area(r)}");

            Rectangle s = new Square();
            s.Width = 8;
            Console.WriteLine($"{s} as area {Area(s)}");
        }
    }
}

Labels:

Comments

Post a Comment

Popular posts from this blog

XML Webservice (ASMX) - SOAP Request and Response Invocation logging

You are an integration developer. Eventualy you came into the state where there is nothing else you can debug, and you have to check which SOAP request it is built on the request, and which SOAP response you are getting from the server. C# XML Webservice (ASMX) - SOAP Request and Response Invocation logging In the legaccy .NET framework System.Web.Services , this means using soapExtensions to help you intersept the interaction with the webservice. This is done like so:  public class TraceExtension : SoapExtension     {         Stream oldStream;         Stream newStream;         string filename;         // Save the Stream representing the SOAP request or SOAP response into          // a local memory buffer.          public override Stream ChainStream(Stream stream)         {           ...
Post a Comment
Read more

Abstract Factory Pattern

Abstract Factory Pattern  Gamma Categorization: Creational Design Patten Summary: When the object construction is complicated, needing multiple arguments, we should create a separate function (Factory Method) or class (Factory), which is responsible for the creation of the all object. Problem examples Suport of multiple databases Multiple data sources: Serial port, ethernet port, device driver Diferent report types Solution Abstract class Generalized interface A Factory creates instances of the concrete classes Sample Code The abstract factory public   interface   IPhotoFactory {      IAnaloguePhoto   CreateAnaloguePhoto ();      IDigitalPhoto   CreateDigitalPhoto (); } The abstract products public   interface   IAnaloguePhoto {      string   GetName (); } public   interface   IDigitalPhoto {      ...
Post a Comment
Read more

SOLID (1/5) - Single Resposibility Principle

 SOLID (1/5) - Single Resposibility Principle The single-responsibility principle (SRP) is a computer-programming principle that states that every class in a computer program should have responsibility over a single part of that program's functionality, which it should encapsulate. All of that module, class or function's services should be narrowly aligned with that responsibility. In the following example we have a TodoList class which only handles it's own functionality logic, and then we have a Persistance class which handles the saving logic, hence keeping the concerns separeted. using   System ; using   System . Collections . Generic ; namespace   Journal {      public   class   TodoList     {          private   readonly   List < string >  _entries  =  new   List < string >();          private...
Post a Comment
Read more