Design Patterns in .NET: Reusable Approaches in C# and F# for Object-Oriented Software Design

© Dmitri Nesteruk 2019

Dmitri NesterukDesign Patterns in .NEThttps://doi.org/10.1007/978-1-4842-4366-4_25

25. Visitor

Dmitri Nesteruk^1 

(1)

St. Petersburg, c.St-Peterburg, Russia

 

To explain this pattern I’m going to jump into an example first and then discuss the pattern itself. Suppose you have parsed a mathematical expression (with the use of the Interpreter pattern, of course) composed of double values and addition operators; for example,

(1.0 + (2.0 + 3.0))

This can expressed using an object hierarchy similar to the following:

public abstract class Expression { /* nothing here (yet) */ }

public class DoubleExpression : Expression

{

  private double value;

  public DoubleExpression(double value) { this.value = value; }

}

public class AdditionExpression ...