Writing access to private objects via public readOnly property

Question

I am currently struggling to understand something i just saw somewhere.

Lets say I have two classes :

 class MyFirstCLass{
      public int membVar1;
      private int membVar2;
      public string membVar3;
      private string membVar4; 

      public MyFirstClass(){
      }
 }

and :

 class MySecondClass{
      private MyFirstClass firstClassObject = new MyFirstClass();

      public MyFirstClass FirstClassObject{
           get{
                return firstClassObject;
           }
      }
 }

If i do something like this :

 var secondClassObject = new MySecondClass(){
      FirstClassObject = {membVar1 = 42, membVar3 = "foo"}
 };

secondClass is an instanciation of MySecondClass, and does have one private member variable of type MyFirstClass wich has a readOnly property. However, i am able to change the state of membVar1 and membVar2. Isn't there any encapsulation problem ?

Best regards,

Al_th

Answer 1

The fact that the FirstClassObject property on MySecondClass has no setter does not mean that the object returned from the getter becomes immutable. Since it has public fields, these fields are mutable. Therefore it is perfectly legal to say secondClassObject.FirstClassObject.membVar1 = 42. The absence of the setter only means that you cannot replace the object reference stored in the firstClassObject field with a reference to a different object.