Functional programming: Closure reference cycle and fix

Here, I will try to explain an example of closure reference cycle. Follow the following article to understand more about closures in swift.

The reference cycle looks rusty !!!
closure reference cycle.
var humanObj:Human? = Human(firstName: “John”, lastName: “Doe”)let fullName = humanObj?.fullNamehumanObj = nil

The fix


A weak reference is a reference that does not keep a strong hold on the instance it refers to, and so does not stop ARC from disposing of the referenced instance. This behaviour prevents the reference from becoming part of a strong reference cycle.

lazy var fullName:() -> String = { [weak self] inguard let weakSelf = self else { return “”}return “\(weakSelf.firstName) \(weakSelf.lastName)”}


Like a weak reference, an unowned reference does not keep a strong hold on the instance it refers to. Unlike a weak reference, however, an unowned reference is used when the other instance has the same lifetime or a longer lifetime

lazy var fullName:() -> String = { [unowned self] inreturn “\(self.firstName) \(self.lastName)”}
lazy var fullName:() -> String = { [unowned unownedSelf = self] inreturn “\(unownedSelf.firstName) \(unownedSelf.lastName)”}

How to capture self with closures having arguments?

Well, you should capture the self before the internal closure parameter or before the parenthesis of internal parameters. Check the code below. It explains how to capture self in a single parameter case. If you have multiple parameters, you may also use parenthesis.

capturing self along with closure parameters

Exceptional cases:

Although it is good practice to capture self weakly in closures, it is not always necessary. Closures that are not retained by the self can capture it strongly without causing a retain cycle. A few common examples of this are:

DispatchQueue.main.async {
self.doSomething() // Not a retain cycle
UIView.animate(withDuration: 1) {
self.doSomething() // Not a retain cycle
lazy var fullName = {
return self.firstName + " " + self.lastName
}() // not retained. no need to use self with weak or unowned

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