Concrete Element Classes (Book and Fruit):?

Short answer: The concrete element classes Book and Fruit implement the IShoppingCartElement interface. Each class has a price and the Accept method that allows the visitor to perform an operation on it. public class Book : IShoppingCartElement

Example code

{
public double Price { get; }
public Book(double price) => Price = price;
public void Accept(IShoppingCartVisitor visitor) => visitor.Visit(this); }
public class Fruit : IShoppingCartElement
{
public double Price { get; }
public Fruit(double price) => Price = price;
public void Accept(IShoppingCartVisitor visitor) => visitor.Visit(this); }

Real-world example (ShopNest)

Use a GoF pattern in ShopNest only when it removes duplication or makes a change safer—explain the problem it solves in the interview.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.