Copied the code below from a tutorial, and I mostly understand what is going on. But I'd like to be able to fully read it.
What I do get is that:
handler can be nil, but here it's the code to run upon the completion of UIAlertAction.
But am unsure what (_) in is. I have also sometimes seen it as [self] in
Thank you
controller.addAction(UIAlertAction(title: "OK", style: .default, handler: { (_) in controller.dismiss(animated: true, completion: nil)}))
But am unsure what (_) in is.
_ means that the var name is hidden.
. Let's explain:
you could write fully expanded syntax:
controller.addAction(UIAlertAction(title: "OK", style: .default, handler: { (action) -> Void in controller.dismiss(animated: true, completion: nil)}))
This would give you a reference to the action: UIAlertAction parameter .
You can also skip -> Void (as you do when you declare a func without return value):
controller.addAction(UIAlertAction(title: "OK", style: .default, handler: { (action) in controller.dismiss(animated: true, completion: nil)}))
And finally, if you don't need access to action, you can replace with _
controller.addAction(UIAlertAction(title: "OK", style: .default, handler: { (_) in controller.dismiss(animated: true, completion: nil)}))
Going even further, you can remove the parenthesis:
controller.addAction(UIAlertAction(title: "OK", style: .default, handler: { _ in controller.dismiss(animated: true, completion: nil)}))
.
I have also sometimes seen it as [self] in
This "captures" self and avoid you to have to write self.someProperty each time you need to access inside the closure to someProperty or func defined of the class (self).
