public Product Apply(Product product, IPrincipal customer)
        {
            var discount = customer.IsInRole("PreferredCustomer") ? .95m : 1;

            return(product.WithUnitPrice(product.UnitPrice.Multiply(discount)));
        }
 public Product Apply(Product product, IPrincipal customer)
 {
     var discount = customer.IsInRole("PreferredCustomer") ? .95m : 1;
     return product.WithUnitPrice(product.UnitPrice.Multiply(discount));
 }