using System;

public class A

{

    public Guid ID { get; set; }    

    public int Bar { get; set; }    

    public override bool Equals(object obj) => obj switch

                                                  {

                                                      A entity => ID.Equals(entity.ID),

                                                      _ => false

                                                  };

    public override int GetHashCode() => ID.GetHashCode();

}

​

​

public class Program

{

    public A Foo { get; set; }

    public Program()

    {

        Foo = new A() { Bar = 10 };

        Foo = new A();

        Console.WriteLine(Foo.Bar);

    }

    public static void Main()

    {

        new Program();

    }

}