I have this customer class:

public class Customer
{
    private List<Invoice> _Invoices = new List<Invoice>();
    public Invoice this[int item]
    {
        get
        {
            return _Invoices[item];
        }
        set
        {
            _Invoices[item] = value;
        }
    }
}

I then do this:

static void Main(string[] args)
{
    Invoice InvA = new Invoice();
    InvA.InvoiceId = "A0001";

    Invoice InvB = new Invoice();
    InvB.InvoiceId = "B0002";

    Customer cust = new Customer();
    cust[0] = InvA;
    cust[1] = InvB;
}

I'm not really seeing a usage for indexers. It seems to me that an Invoices collection would be better. What's the point of indexers?