I overloaded the == operator on my class as follows:
public static bool operator ==(Table pt1, Table pt2) { return Compare(pt1, pt2) == 0 && pt1.TableName == pt2.TableName; } Compare will work just as the strcmp does in c++, returning an integer. Problem is that if I do an if (MY_CLASS == null), it will call my == operator, and thus my Compare function. What is the alternatiev? to put an check on pt1 and pt2 to see if they are null? Or just in pt2?
You should checkout Microsoft's guidelines for implementing the '==' operator and also for overriding 'Equals()'.
Adapting their example you'd want something like:
public static bool operator ==(Table a, Table b) { // If both are null, or both are same instance, return true. if (System.Object.ReferenceEquals(a, b)) { return true; } // If one is null, but not both, return false. if (((object)a == null) || ((object)b == null)) { return false; } // Return true if the fields match: return Compare(a, b) == 0 && a.TableName == b.TableName; } 
You will need the null checks to get the correct behaviour. The clearest way to add this check in my opinion is to call object.ReferenceEquals(x, null), since it is a straight non-polymorphic method call and presumably fairly efficient.
Just add this line to your operator:
if ((object)pt1 == null || (object)pt2 == null) return false; The (object) cast is there to prevent recursion (from calling object.== instead of MY_CLASS.==.
Although I'm not sure of the conditions that should arise when comparing null to null.
I asked a similar question here. Have a look at it.
public bool Equals(ClauseBE other) { if (this._id == other._id) { return true; } return false; } public override bool Equals(Object obj) { if (obj == null) { return base.Equals(obj); } if (!(obj is ClauseBE)) { throw new InvalidCastException("The 'obj' argument is not a ClauseBE object."); } return Equals(obj as ClauseBE); } public override int GetHashCode() { return this._id.GetHashCode(); } public static bool operator ==(ClauseBE a, ClauseBE b) { if (ReferenceEquals(a, null) && ReferenceEquals(b, null)) { return true; } if (ReferenceEquals(a, null) || ReferenceEquals(b, null)) { return false; } return a.Equals(b); } public static bool operator !=(ClauseBE a, ClauseBE b) { return !(a == b); } 
