Hands-On Design Patterns with C# and .NET Core

Liskov substitution principle

Being able to substitute objects at runtime is the basis of the Liskov substitution principle. In OOP, if a class inherits from a base class or implements an interface, then it can be referenced as an object of the base class or interface. This is easier to describe with a simple example.

We'll define an interface for an animal and implement two animals, Cat and Dog, as follows:

interface IAnimal{     string MakeNoise();}class Dog : IAnimal{   public string MakeNoise()     {        return "Woof";     }}class Cat : IAnimal{    public string MakeNoise()    {        return "Meouw";    }}

Then we can refer to the Cat and Dog as an animal as follows:

var animals = new List<IAnimal> { new Cat(), new Dog() };foreach(var animal in animals){ Console.Write(animal.MakeNoise()); ...