How can I overload the “==” operator to determine of two ID numbers are the same?

Question

I need to write a method that will take two employee objects as input parameters and compare their ID's to determine whether or not they match.

It's incomplete at the moment; but so far, I have an Employee class that inherits first and last name properties from a "Person" class, and has ID as its own property. I'm writing the method in the employee file and have already instantiated 2 example employees in my program. As for overloading the ==, I'm running into an error that says "Employee" defines operator == but does not override Object.Equals." It also says I need to define "!=", but I'm confused on how to set up the != overload when it doesn't even figure into this method.

I've seen two ways of doing a compare method, one that returns true or false, and another that simply writes "match" to the console. Either of those would work for my purposes, but I can't figure out a workaround for the errors or how I'd change the code in this situation in order to determine a match between 2 employee ID's. Here is my code below; I'd appreciate any input on what may be going wrong! (I have a feeling it may be very off). I'm also unsure of how to call the method but I'm currently trying to figure it out.

Program file:

namespace OperatorOverload
{
    class Program
    {
        static void Main(string[] args)
        {
            Employee example = new Employee();

            example.FirstName = "Kitty";
            example.LastName = "Katz";
            example.ID = 24923;

            Employee example2 = new Employee();
            example2.FirstName = "John";
            example2.LastName = "Dudinsky";
            example2.ID = 39292;

            Console.ReadLine();
        }
    }
}

Employee Class:

namespace OperatorOverload
{
    class Employee : Person
    {
        public int ID { get; set; }

        public static bool operator==(Employee employee, Employee employee2)
        {
            if (employee.ID == employee2.ID)

                return true;        
            else           
                return false;
            }
        }
    }

Person Class:

namespace OperatorOverload

{
    public class Person
    {
       public string FirstName { get; set; }
        public string LastName { get; set; }      
    }
}

Answer 1

you need to also override the Equals method:

public override bool Equals(Object Obj)
{
    Person person = obj as Person;

    if(person == null)
        return false;

    return this.ID.Equals(person.ID);
}

Microsoft's recommandations :

Implement the GetHashCode method whenever you implement the Equals method. This keeps Equals and GetHashCode synchronized.

Override the Equals method whenever you implement the equality operator (==), and make them do the same thing.

Answer 2

What You need to do is to use the Equals function and override it like this:

public override bool Equals(object obj)
{
    var item = obj as Employee;

    if (item == null)
    {
        return false;
    }

    return this.ID.Equals(item.ID);
}

Answer 3

The compiler is basically telling you that if you want to overload the == operator for the class Employee you will also have to override Object.Equals method and the != operator so that you will get a consistent semantic which you can use to compare instances of type Employee.

This means that you must not look for workarounds: you just have to overload the != operator and override Object.Equals so that Employee objects are compared by ID and not by reference (as they do by default if you don't provide your own equality semantic).

Answer 4

You should use this class. Override operator!=, operator== and Equals(object) method.

class Employee : Person
    {
        public int ID { get; set; }

        public static bool operator ==(Employee employee, Employee employee2)
        {
            if (employee.ID == employee2.ID)
                return true;
            else
                return false;

            //but you should use 
            //return employee.ID == employee2.ID;
        }

        public static bool operator !=(Employee employee, Employee employee2)
        {
            return employee.ID != employee2.ID;
        }

        public override bool Equals(object obj)
        {
            var emp = obj as Employee;
            if (emp == null)
                return false;

            return this.ID.Equals(emp.ID);
        }
    }

Answer 5

This is a better way to override a Equals method:

public override bool Equals(object obj)
{
    if (obj is null) return false;
    if (ReferenceEquals(this, obj)) return true;
    if (obj.GetType() != this.GetType()) return false; //optional. depends on logic
    return this.ID.Equals(((Employee)obj).ID);
}