Do we have a retention cycle when a class (middle of hierarchy) is removed?

Question

Situation: Class A (Grandparent class) retains class B (Parent class) and class B(Parent class) retains class C(Child class) then If I removed class B then what would happen, Does class A and class C has a retention cycle and cause memory leaks?

Answer 1

Depends on how did you remove the Class B.

If I removed class B then what would happen

What do you mean by that ? If you are using ARC, you are not supposed to call release. So how did you removed the class B then?

Because Class A is holding the strong reference to class B, class B's retain count is 1. Now the only way you can bring the refrence count of Class B to 0 and let the ARC clean Class B is by setting the strong reference of Class B to nil.

So, if in your class A if you say,

self.classBReference = nil;

Then Class B's reference count becomes 0 and obviously class B gets deallocated and because Class B gets deallocated the reference count of class C becomes 0 because Class C was strongly held by class B and class B no longer exists. Hence Class C is now becomes the candidate to be removed by ARC.

Proof Of Concept :

Here is my class Declaration

class A {
    var binstance : B? = B() //Declared as optional because I need to set the reference to nil later :)

    deinit {
        print("A deinited")
    }
}

class B {
    var cinstance = C()

    deinit {
        print("B deinited")
    }
}

class C {
    deinit {
        print("C deinited")
    }
}

Now I create instance of Class A in my VC, as a result A,B and C will all have reference count of 1.

var ainstance : A = A()

When I set the ainstance to nil here is the sequence of calls

self.ainstance.binstance = nil

O/P

B deinited

C deinited