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 { getset; }        
        public virtual int Height { getset; }

        public Rectangle()
        {

        }

        public Rectangle(int widthint 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)}");
        }
    }
}

Comments

Popular posts from this blog

C# Extension Methods

 C# Extension Methods Extension methods      public   static   class   ExtensionMethods     {          public   static   Stopwatch   Measure ( this   Func < int >  f )         {              var   sw  =  new   Stopwatch ();              sw . Start ();              f ();              sw . Stop ();              return   sw ;         }          public   static   void   Save ( this   ISerializable   s...

SOLID (4/5) - Interface segregation principle

Interface segregation principle In the field of software engineering, the interface-segregation principle (ISP) states that no client should be forced to depend on methods it does not use. ISP splits interfaces that are very large into smaller and more specific ones so that clients will only have to know about the methods that are of interest to them. Such shrunken interfaces are also called role interfaces. ISP is intended to keep a system decoupled and thus easier to refactor, change, and redeploy. using   System ; namespace   interfacesegregation {      public   class   Document       {     }      public   interface   IMachine       {          void   Print ( Document   d );          void   Scan ( Document   d );     ...

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...