Visitor Design Pattern in C#

The Visitor Pattern is a behavioral design pattern that allows you to add further operations to objects without having to modify them. It is particularly useful when you have a structure of objects and you want to perform operations on these objects that can be defined outside of their classes. This pattern follows the Open/Closed Principle by allowing new functionality to be added without altering the existing code.

The Visitor Design Pattern should be used when you have distinct and unrelated operations to perform across a structure of objects (element objects). That means the Visitor Design is used to create and perform new operations on a set of objects without changing the object structure or classes.

Components of Visitor Pattern

1. Visitor Interface: Declares a Visit method for each type of ConcreteElement in the object structure.
2. ConcreteVisitor: Implements the Visitor interface and defines the actions for each type of ConcreteElement.
3. Element Interface: Declares an Accept method that takes a Visitor as an argument.
4. ConcreteElement: Implements the Element interface and defines the Accept method to call the Visitor's method.
5. Object Structure: Can be a collection or a composite of elements which can be iterated to apply the Visitor.

State Design Pattern in C#

The State Design Pattern is a behavioral design pattern that allows an object to alter its behavior when its internal state changes. This pattern is particularly useful for implementing state machines and ensuring that the object’s behavior remains manageable and modular.

This pattern is useful when an object needs to go through several states, and its behavior differs for each state. Instead of having conditional statements throughout a class to handle state-specific behaviors, the State Design Pattern delegates this responsibility to individual state classes.

Components of State Desgin Pattern

1. Context: This is the class that contains an instance of a state and delegates state-specific behavior to the current state object.
2. State: An interface that encapsulates the behavior associated with a particular state of the Context.
3. Concrete States: Classes that implement the State interface, each representing a specific state and defining its behavior.