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?

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()` — nhgrif, Jul 16 '15 at 12:47
Please check this question there is `[unowned self]` in swift : http://stackoverflow.com/questions/24320347/shall-we-always-use-unowned-self-inside-closure-in-swift and https://dhoerl.wordpress.com/2013/04/23/i-finally-figured-out-weakself-and-strongself/ — Ashish Kakkad, Jul 16 '15 at 12:51

score 33 · Accepted Answer · answered Jul 16 '15 at 13:36

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.

You can also substitute `if let` with `guard let` here to avoid another nesting (indentation) level: `guard let strongSelf = self else { return }` — Jonathan Cabrera, Aug 09 '18 at 18:16

Sentry.co · Answer 2 · 2019-10-14T05:35:39.500

16

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

edited Oct 14 '19 at 05:35

answered Apr 10 '19 at 12:16

Sentry.co

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score 7 · Answer 3 · answered Dec 02 '16 at 13:19

7

another way to use weak selfwithout using strongSelf

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

answered Dec 02 '16 at 13:19

Cruz

2,602
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8

I love this BUT be careful. Chris Lattner has specifically stated this is a compiler bug https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160118/007425.html – wuf810 Jan 31 '17 at 19:21

score 5 · Answer 4 · answered Jul 16 '15 at 15:14

5

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()

answered Jul 16 '15 at 15:14

GoZoner

67,920
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score 1 · Answer 5 · answered Jul 16 '15 at 13:19

1

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.

answered Jul 16 '15 at 13:19

s1ddok

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What is the correct way of use strongSelf in swift?

5 Answers5

Swift 4.2