Swift: Why int! member instance change to int? in block?

Question

I defined a member instance frameCount which type is Int!, But when I reference it in block it's type become Int?. If I doesn't unwrap it Xcode will prompt complie error "Value of optional type 'Int?' not unwrapped; did you mean to use '!' or '?'?".

I can use it without unwrapping out of block.

//Without unwrapping
self.frameCount = self.frameCount + 1
optQueue.async { [weak self] in
    //frameCount become Int?.
    //If I doesn't unwrap it Xcode will prompt complie error "Value of optional type 'Int?' not unwrapped; did you mean to use '!' or '?'?"
    self?.frameCount = (self?.frameCount)! + 1;
}

It's not solves your problem, but you should read this and restrain from using IUO. — user28434'mstep
– user28434'mstep, Commented Aug 30, 2018 at 14:12
If async is a GCD API [weak self] is pointless. GCD dispatch queues don't cause retain cycles. And don't misuse IUO. — vadian
– vadian, Commented Aug 30, 2018 at 14:26

Rakesha Shastri · Accepted Answer · 2018-08-30 14:10:01Z

3

Your variable is not optional! Your self is. Since you are doing an asynchronous call, by the time completion is executed self might cease to exist. That is why you are capturing it as weak. But if you want it run compulsorily, you could remove the [weak self], but it will hold a strong reference to self and prevent it form being deallocated. So if your completion is not called, it'll never get deallocated.

answered Aug 30, 2018 at 14:10

Rakesha Shastri

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Shehata Gamal · Accepted Answer · 2018-08-30 14:20:18Z

2

Here self is optional not frameCount , you can use guard to avoid this as you may have a lot of stuff that need to access self instead of force-unwrapping them all

optQueue.async { [weak self] in
   guard let strongSelf = self else { return }
   strongSelf.frameCount += 1
}

answered Aug 30, 2018 at 14:20

Shehata Gamal

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Georgy Fesenko · Accepted Answer · 2018-08-30 17:47:57Z

1

Also you can replace weak self with unowned self, so you will still have a weak reference to self, but not optional one.
However, be careful with that approach, it could lead to a crash if self will be deallocated earlier than completion will be executed.

optQueue.async { [unowned self] in
    self.frameCount = self.frameCount + 1
}

answered Aug 30, 2018 at 17:47

Georgy Fesenko

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