Objective-c: why private ivars are not hidden from the outside access when using KVC

Question

After trying to access ivars using KVC, I have noticed that there was no protection on private and protected ivars. It doesn\'t matter what I put a in front of the ivar (pri

Answer 1

I'll add my two cents to this old question.

I think the @private, @protected is there also to prevent access to a variable using the '->' operator.

Imagine you have a iVar called myPrivateVar declared like below:

@interface MyClass:NSObject{
  @public
    NSArray *myPrivateVar;
}

So even if you implement the below class method to return NO and don't have accessors declared for the iVar:

+accessInstanceVariablesDirectly{
    return NO;
}

the variable is still accessible if you use myClassObj->myPrivateVar;

On the other hand if you just make the @public to @private and don't implement accessInstanceVariableDirectly, the variable is still accessible by using KVC:

[myClassObj valueForKey:@"myPrivateVar"];

(and not accessible via myClassObj->myPrivateVar)

So to make your iVar completely private it should be declared as @private and also accessInstanceVariablesDirectly should be implemented to return NO.