When should we use neither [Weak Self] nor [Owned Self]?

You need to use [weak self] or [unnamed self] if closing could result in a "strong reference cycle".

If this can happen by assigning a capped property to self , you are referring to self or property self that closes itself. Closures are reference types, so essentially the same rules apply to strong references as you would with normal classes.

In the case of your example, no [weak self]or [unowned self], since you don't need to assign the closure to a variable inside the class you're selfreferencing , there won't be a strong reference cycle.

For more information, check out the Strong Closure Reference Loops section of the Swift Programming Language Guide . Here's an example from the above link when a strong reference cycle might be due to closures:

class HTMLElement {

    let name: String
    let text: String?

    lazy var asHTML: () -> String = {
        if let text = self.text {
            return "<\(self.name)>\(text)</\(self.name)>"
        } else {
            return "<\(self.name) />"
        }
    }

    init(name: String, text: String? = nil) {
        self.name = name
        self.text = text
    }

    deinit {
        print("\(name) is being deinitialized")
    }

}

If not [unowned self]in the closure asHTML, assigning to the closure will result in a strong reference cycle asHTML. Changing the implementation to the asHTMLfollowing fixed the issue:

lazy var asHTML: () -> String = {
    [unowned self] in
    if let text = self.text {
        return "<\(self.name)>\(text)</\(self.name)>"
    } else {
        return "<\(self.name) />"
    }
}