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 ==.
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.)
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.
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; }
}
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.
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
I implemented the following and it 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);
}