Swift: Strong, Weak, and Unowned Reference Explained

Swift: Strong, Weak, and Unowned Reference Explained

In the world of iOS development, strong, weak, and unowned references are essential for memory management. Understanding how each works is critical for a successful app. In this blog post, we’ll explore all three types of reference and learn how to use them in Swift.

A strong reference keeps a strong hold on an object and prevents it from being deallocated. When you create a strong reference, you are telling ARC that you want to keep the object alive. As long as one or more strong references are pointing to an object, it will remain in memory.

The most common type of reference in Swift is a strong reference. When you create a variable or constant and assign it a value, you are creating a strong reference. For example:

let myObject = MyObject()

In the code above, we have created a strong reference to the instance of MyObject. As long as this reference is not broken, the object will remain in memory.

A weak reference is the opposite of a strong reference. It does not keep a strong hold on the object and does not prevent it from being deallocated. A weak reference is useful when you want to refer to an object without keeping it alive.

To create a weak reference, you must mark it with the weak keyword. For example:

weak var myObject = MyObject()

In the code above, we have created a weak reference to the instance of MyObject. Since the reference is weak, it will not keep the object alive. If all other strong references to the object are broken, the object will be deallocated.

An unowned reference is similar to a weak reference, but it does not become nil when the object it refers to is deallocated. An unowned reference is useful when you know that the object will always exist. For example, if you create a view controller, you know that it will always have a view. To create an unowned reference, you must mark it with the unowned keyword. For example:

unowned let myViewController = MyViewController()

In the code above, we have created an unowned reference to the instance of MyViewController. Since the reference is unowned, it will not become nil when the view controller is deallocated.

In summary, understanding strong, weak, and unowned references is critical for successful memory management in Swift. Strong references keep an object alive, weak references allow an object to be deallocated, and unowned references do not become nil when the object they refer to is deallocated. Knowing when to use each type of reference will help you create better apps in Swift.