Swift uses Automatic Reference Counting (ARC) to manage memory. ARC allocates and frees up memory for instances as needed. Developers must tell ARC about relationships between classes to avoid crashes from accessing deallocated instances. Strong references keep instances in memory while they are used. Weak and unowned references avoid strong reference cycles that prevent deallocation. Closures that capture class instances can also cause strong reference cycles.

1. Memory Management In Swift

2. Swift uses ARC • ARC allocates memory for new instances. • ARC frees up memory when instance is no longer needed. • Tell ARC how are the relationships between your classes. • Accessing deallocated instances will crash your app :( • Deallocated = 0 reference counting

3. Assigning a class instance to variable, constant or property will make a strong reference. It will remain as long as you use it. Like using a leash (strong reference) with a dog, it can't run away!

4. "Strong Reference Cycle" When two Instances hold strong reference to each other.

5. Solution ! Define one of the references as "weak" or "unowned"

6. Weak *Doesn't keep strong reference to instance *Set to nil if the referenced instance is deallocated *Use it with delegate (Optional delegate)

7. Unowned *Doesn't keep strong reference to instance *Become dangling pointer(cause crash if accessed) when the referenced instance is deallocated *Assumed to always have a value *Same as "assign" in Objective-c

8. Strong Reference Cycle can also occur if you assign a closure to a property of a class instance, and the body of that closure captures the instance

9. Thanks References http://goo.gl/PJUX7f By Hossam Ghareeb