What is the correct way of use strongSelf in swift?

Question

In Objective-C in non-trivial blocks I noticed usage of weakSelf/strongSelf.

What is the correct way of usage strongSelf in Swift? Something like:

if let strongSelf = self {
  strongSelf.doSomething()
}

So for each line containing self in closure I should add strongSelf check?

if let strongSelf = self {
  strongSelf.doSomething1()
}

if let strongSelf = self {
  strongSelf.doSomething2()
}

Is there any way to make aforesaid more elegant?

Downhaul

There's nothing special about strongSelf here. It's just a variable name. Perhaps add the Objective-C code you're hoping to replicate? What you're doing here is no different from simply self?.doSomething() – Accustomed

Please check this question there is [unowned self] in swift : #24320847 and dhoerl.wordpress.com/2013/04/23/… – Takao

Answer 1

Using strongSelf is a way to check that self is not equal to nil. When you have a closure that may be called at some point in the future, it is important to pass a weak instance of self so that you do not create a retain cycle by holding references to objects that have been deinitialized.

{[weak self] () -> void in 
      if let strongSelf = self {
         strongSelf.doSomething1()
      }
}

Essentially you are saying if self no longer exists do not hold a reference to it and do not execute the action on it.

Underdone

You can also substitute if let with guard let here to avoid another nesting (indentation) level: guard let strongSelf = self else { return } – Fuze

Answer 2

Swift 4.2 🔸

guard let self = self else { return }

Ref: https://benscheirman.com/2018/09/capturing-self-with-swift-4-2/
Ref2: https://www.raywenderlich.com/5370-grand-central-dispatch-tutorial-for-swift-4-part-1-2

Halifax

Answer 3

another way to use weak selfwithout using strongSelf

{[weak self] () -> void in 
      guard let `self` = self else { return }
      self.doSomething()
}

Satiety

I love this BUT be careful. Chris Lattner has specifically stated this is a compiler bug lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160118/… – Tropo

Answer 4

Your use of strongSelf appears to be directed at only calling the doSomethingN() method if self is not nil. Instead, use optional method invocation as the preferred approach:

self?.doSomethingN()

Poteen

Answer 5

If you use self in your closure it is automatically used as strong.

There is also way to use as weak or unowned if you trying to avoid a retain cycles. It is achieved by passing [unowned self] or [weak self] before closure's parameters.

Succinct