接口实现是一条路要走，我会实现Discount类之间的接口，我会强制DiscountNode类实现接口，你可以在下面找到一个例子：

using System;

namespace StackOverflow
{
    internal class Program
    {
        static void Main(string[] args)
        {
            var discountCodeBxgy = new DiscountCodeBxgy() { Code = "Bxgy" };

            var discountCodeNode = new DiscountCodeNode { Id = "MyId", CodeDiscount = discountCodeBxgy };

            if (discountCodeNode.CodeDiscount is DiscountCodeBxgy Bxgy)
            {
                Console.WriteLine(Bxgy.Code);
            }
            // Just to prove it is right! --> this message will not be shown in the console app
            if (discountCodeNode.CodeDiscount is DiscountCodeApp App)
            {
                Console.WriteLine(App.Code);

            }

            Console.ReadLine();
        }

       
    }

    internal class DiscountCodeNode
    {
        public IDiscountCode CodeDiscount { get; set; }
        public string Id { get; set; }
    }

    internal class DiscountCodeApp : IDiscountCode
    {
        public string Code { get; set; }

    }

    internal class DiscountCodeBasic : IDiscountCode
    {
        public string Code { get; set; }

    }

    internal class DiscountCodeBxgy: IDiscountCode
    {
        public string Code { get; set; }

    }

    internal class DiscountCodeFreeShipping : IDiscountCode
    {
        public string Code { get; set; }

    }
    internal interface IDiscountCode
    {
        string Code { get; set; }
    }
}

最后，由于模式匹配，您将在控制台中输出“Bxgy”，这意味着它已经工作，如下图所示：

希望能帮上忙
问候
米格尔