What is difference between "[self] in" & "[weak self] in" in Swift?

Question

I just found out that I can write "[self]" in the closures instead of [weak self] in but I'm not sure if it is safe or not.

more detail:

Before:

func roundShape(corners: CACornerMask, radius: CGFloat) {
        DispatchQueue.main.async { [weak self] in
            layer.cornerRadius = radius
            layer.maskedCorners = corners
        }
    }

Now:

 func roundShape(corners: CACornerMask, radius: CGFloat) {
      DispatchQueue.main.async { [self] in
           layer.cornerRadius = radius
           layer.maskedCorners = corners
      }
  }

So please light me up if you know the difference.

Answer 1

Writing [self] is same as leaving the closure as it is meaning it could cause retain cycle unlike [weak self] , BTW no need for any of them with DispatchQueue.main.async { as GCD queues don't hold a strong reference to self

Answer 2

Weak self is a concept of ARC, which is mainly used to avoid retain cycle. If you directly use self, then it creates a strong reference and will not be removed from the memory. Consequently, the object that holds the variable will stay alive and leads to memory leakage. In order to overcome this issue, weak self must be used, which instantly releases the memory once the job is done.

Note: Weak self is an Optional so you can use optional chaining to access variables.