operator overload problem

Question

I am trying to write operator overload for custom class and don't know how to handle null comparison.

Class Customer
{
    int id;

    public static bool operator ==(Customer a, Customer b)
    {
        //When both a and b are null don't know how to compare as can't use == in here as
        //it will fall into loop
    }
}

Problem is when a and b both are null result is true but not sure how to check it without using ==.

Answer 1

I'm not 100% sure I understand the problem, but you should be able to do:

if (((object)a == null) && ((object)b == null)) { return true; }

Without any problems.

Answer 2

if (Object.ReferenceEquals(a,b))
     return true;

ReferenceEquals() checks if they are pointing to the exact same object (or if they are both null)

(As a general rule, it's good to start an Equals() method with a call to ReferenceEquals, particularly if the rest of the method is complicated. It will make things like a==a quickly return true, instead of having to check every element.)

Answer 3

I usually use object.Equals(a, b).

In your case:

public static bool operator ==(Customer a, Customer b)
{
    if(object.Equals(a, null) && object.Equals(b, null)
    { return true; }
}

Answer 4

any of the following

 object.ReferenceEquals(a, null)
 object.Equals(a, null)
 (object)a == null;

PS. I think this is probably better off in Customer.Equals, and having == rely on that.

Answer 5

Is it possible to cast them to system.object and use the == operator to check if it's null? I'd check it but I'm not on a dev machine

Answer 6

Thanks a bunch guys,

I implemented following and works like champ

public static bool operator ==(Customer a, Customer b)

{

if(object.ReferenceEquals(a,b)
{ return true; }
else if(((object)a == null) || ((object)b == null))
     {return false;}
else if(a.Id == b.Id)
     {return true;}

return false;

}

public static bool operator !=(Customer a, Customer b) { return !(a==b); }