### **Visitor Pattern**

**Description:**
The Visitor Pattern allows you to add new operations to existing object
structures without modifying their classes. It separates an algorithm from the
object structure on which it operates, enabling new operations to be added
without altering the classes of the elements.

**How and When to Use It:**
- **When to Use:** Use the Visitor Pattern when you need to perform operations
on objects of different types within a complex object structure and you want to
keep related operations together without modifying the objects themselves.

- **Example:** In a file system crawler, a visitor can perform operations like
calculating total size, indexing files, or checking permissions as it visits
each file or directory object.