using System;

using System.Collections.Generic;

​

public class Address

{

    public string Street { get; set; }

    public string City { get; set; }

    public string State { get; set; }

    public string Zip { get; set; }

}

​

public class Person

{

    public string Name { get; set; }

    public int Age { get; set; }

    public float HeightInInches { get; set; }

    public Dictionary<string, Address> Addresses { get; set; }

}

​

// 🔴 Incorrect, this will fail to detect destroyed or missing objects.

public class NullTest<T>

{

    public bool IsNull { get; }

​

    public NullTest(T value) => IsNull = value == null;

}

​

// 🟢 Correct

public class NullTestCorrect<T> where T : BaseObj

{

    public bool IsNull { get; }

​

    public NullTestCorrect(T value) => IsNull = value == null;

}

​

public class BaseObj

{

    public static bool operator ==(BaseObj lhs, BaseObj rhs)

    {

        return CompareBaseObjects(lhs, rhs);

    }

​

    public static bool operator !=(BaseObj lhs, BaseObj rhs)

    {

        return !(lhs == rhs);

    }

​

    public override bool Equals(object other)

    {

        BaseObj otherAsObject = other as BaseObj;

        // A UnityEngine.Object can only be equal to another UnityEngine.Object - or null if it has been destroyed.

        // Make sure other is a UnityEngine.Object if "as Object" fails. The explicit "is" check is required since the == operator

        // in this class treats destroyed objects as equal to null

        if (otherAsObject == null && other != null && !(other is BaseObj))

            return false;

        return CompareBaseObjects(this, otherAsObject);

    }

​

    static bool CompareBaseObjects(BaseObj lhs, BaseObj rhs)

    {

        bool lhsNull = ((object)lhs) == null;

        bool rhsNull = ((object)rhs) == null;

​

        if (rhsNull && lhsNull) return true;

        Console.WriteLine(nameof(CompareBaseObjects));

        return true; /* fake is null */

    }

​

    public override int GetHashCode()

    {

        Console.WriteLine(nameof(GetHashCode));

        return 0;

    }

}

​

public class MyObj : BaseObj

{

}

​

​

public class Program

{

    // 🔴 Incorrect, this will fail to detect destroyed or missing objects.

    public static bool NullTestMethod<T>(T value) => value == null;

​

    // 🟢 Correct

    public static bool NullTestMethodConstrained<T>(T value) where T : BaseObj => value == null;

​

    public static void Main()

    {

        Console.WriteLine("Null Test:");

        Console.WriteLine(new NullTest<MyObj>(new MyObj()).IsNull);

        Console.WriteLine();

        Console.WriteLine("Null Test Correct:");

        Console.WriteLine(new NullTestCorrect<MyObj>(new MyObj()).IsNull);

        Console.WriteLine();

        Console.WriteLine();

        Console.WriteLine("Null Test Method:");

        Console.WriteLine(NullTestMethod(new MyObj()));

        Console.WriteLine();

        Console.WriteLine("Null Test Correct Method:");

        Console.WriteLine(NullTestMethodConstrained(new MyObj()));

    }

}