How to instantiate derivative nested class

Question

I am trying to get a object structure such that when someone calls base.two.three.four...seven seven is a getter that would get the value as well as logically inherit values the previous levels. I am trying to figure out how to accomplish this with C# as different variations that I've tried I get a stack overflow or unhandled exception. I remember this being easier with Java. The following is just basic code to acomplish a couple levels:

using System;

public class Program
{
   public static void Main()
   {
       test test = new test();

       Console.WriteLine(test.a);
       Console.WriteLine(test.Ic.a);
       Console.WriteLine(test.Ic.b);
   }
}

public class test
{
   public test()
   {
   }

   public testinner Ic {get;set;}

   public int a = 1;

   public class testinner : test
   {
       public testinner()
       {
           a = 3;
       }

       public int a {get;set;}
       public int b = 2;

   }

}

When I run this I get:

Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
at Program.Main()
Command terminated by signal 6

Console.WriteLine(test.a); Correctly outputs 1, but the error occurs starting at the following lines:

Console.WriteLine(test.Ic.a);
Console.WriteLine(test.Ic.b);

The output is supposed to be: 1 3 2

How do I resolve this?

Jayraj Chhaya · Answer

Hi Mackenzie Thomas, Problem The problem lies in the way the testinner class is defined. It inherits from the test class, but it also contains a property of type test called Ic . This creates a circular reference between the two classes, leading to a stack overflow exception. Cause The cause of the issue is the circular reference between the test and testinner classes. When an instance of testinner is created, it tries to create an instance of test as its property Ic . However, since test already contains an instance of testinner , this leads to an infinite loop of creating instances, resulting in a stack overflow exception. Solution To resolve this issue and achieve the desired object structure, you can modify the code as follows: using System; public class Program { public static void Main() { test test = new test(); Console.WriteLine(test.a); Console.WriteLine(test.Ic.a); Console.WriteLine(test.Ic.b); } } public class test { public test() { Ic = new testinner(); } public testinner Ic { get; set; } public int a = 1; public class testinner { public testinner() { a = 3; } public int a { get; set; } public int b = 2; } } In the modified code, the test class now initializes the Ic property with a new instance of testinner in its constructor. This breaks the circular reference and ensures that the Ic property is properly initialized.

Subarta Ray · Answer

Hi Mackenzie , The issue in your code is related to the fact that the test.Ic property is null when you try to access its properties ( a and b ). You need to instantiate an instance of the testinner class and assign it to the Ic property before accessing its properties. Here's an updated version of your code that resolves the issue: using System; public class Program { public static void Main() { test test = new test(); Console.WriteLine(test.a); // Instantiate testinner and assign it to the Ic property test.Ic = new test.testinner(); Console.WriteLine(test.Ic.a); Console.WriteLine(test.Ic.b); } } public class test { public test() { } // Use private backing field for Ic property private testinner _ic; public testinner Ic { get { // Lazily initialize Ic if it's null if (_ic == null) { _ic = new testinner(); } return _ic; } set { _ic = value; } } public int a = 1; public class testinner : test { public testinner() { a = 3; } public int a { get; set; } public int b = 2; } } In this updated code: I added a private backing field _ic for the Ic property. I modified the get accessor of the Ic property to lazily initialize _ic if it's null. In the Main method, I explicitly instantiate an instance of testinner and assign it to the Ic property before accessing its properties. This should resolve the NullReferenceException issue, and the output should be: 1 3 2