A variation of shopping cart DTOs that violate C# naming standards for properties.

ShoppingCartDtos1.cs

public abstract class ShoppingCart 
{
  public ShoppingCart(string state) 
  {
    _state = state;
  }

  public string _state { get; }
}

public class EmptyCart : ShoppingCart
{
  public EmptyCart() : base("empty") {}
}

public class ActiveCart : ShoppingCart
{
  public ActiveCart() : base("active") { }
  public Item[] unpaidItems { get; set; }
}

public class PaidCart : ShoppingCart
{
  public PaidCart() : base("paid") {}
  public object[] paidItems { get; set; }
  public Money payment { get; set; }
  public string timestamp { get; set; }
}

public class Item 
{
  public string id { get; set; }
  public string title { get; set; }
  public string description { get; set; }
}

public class Money 
{
  public float amount { get; set; }
  public string currency { get; set; }
}