What is the difference between strong, weak, and unowned?

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Main Source: 🔗 Ace the iOS Interview

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TL/DR

Please see the previous answer’s explanation of Automatic Reference Counting.

All of these keywords are different ways of describing how one object maintains a reference to another object.

strongis the default keyword in iOS and will incrementthe reference count of whatever object it’s referring to.

weak does not increment the reference count and the object it references can be nil. This is commonly used when working with delegates.

unowned does not increment the reference count either,but promises that the value it references will not be nil during its lifetime.