koobas.hobune.stream
Is there a difference between these null checks?
After reading this unity article about unity specific null checks I was wondering about shorthand null checks for unity objects. I never found a definitive answer on the forums or documentation so I decided to ask here. Is there a difference between:
if(_myObject)
and
if(_myObject != null)
and
if(!_myObject == null)
I know the last one doesn't make a lot of sense but I decided to add it for completeness sake. Will these ways of checking if a unity object is null always return the same values? Is there a difference in performance? Or are they exactly the same under the hood?
Here is the actual implementation of UnityEngine.Object
public static bool operator==(Object x, Object y) { return CompareBaseObjects(x, y); }
public static bool operator!=(Object x, Object y) { return !CompareBaseObjects(x, y); }
// Does the object exist?
public static implicit operator bool(Object exists)
{
return !CompareBaseObjects(exists, null);
}
static bool CompareBaseObjects(UnityEngine.Object lhs, UnityEngine.Object rhs)
{
bool lhsNull = ((object)lhs) == null;
bool rhsNull = ((object)rhs) == null;
if (rhsNull && lhsNull) return true;
if (rhsNull) return !IsNativeObjectAlive(lhs);
if (lhsNull) return !IsNativeObjectAlive(rhs);
return lhs.m_InstanceID == rhs.m_InstanceID;
}
As you can see:
• if(_myObject) will call implicit operator bool which basically checks whether _myObject is null using CompareBaseObjects
• if(_myObject != null) will call bool operator!= which calls CompareBaseObjects too
However, your last condition will "throw" a cs0472 warning since !_myObject returns a bool, and comparing a bool against null does not make sense.
So the third check would have to be if(!(_myObject == null)) for it to make sense?
Indeed. And it would be very similar to the 2nd example. You just invert the result returned by the overload of the == operator.
Note that Unity has a reference github repository with the source code of the UnityEngine dll. The bool type conversion operator and the two comparison operators can be found there.
Please keep in $$anonymous$$d that this repository is not open source. It's just there for reference. Make sure you read the license before extracting or using any code from there.
