Deep Copy and Shadow Copy in Objective C


Cong's iOS Study Note

I would like to share with you guys this topic which has bothered me so many times before and we all should pay special attention to.

Let’s do an experiment first.

I would create a Class called Person, set 2 properties as “Name” and “Age”.

Then in the main file, I create three reference of person.

Then if I changed the age of the personA, guess what happened? All of the ‘age’ property for those three people has changed!  Let’s look into the memory to see what exactly happened

Screen Shot 2015-06-07 at 6.05.52 PM

Here, we can see that all the three person’s memory address are identical, which we say that personB and personC are the Shadow Copy of personA. They are all the pointers pointing to the same memory address. So we can treat them as personA’s alias.  When you use personB = personA, you are not passing all the properties of the personA to the…

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