From Swift 1.2 onwards we have three ways of performing typecasts:
as is used for typecasts that will always succeed (e.g.
someString as NSString),
as? is used for typecasts that might fail (e.g.
someView as? UIImageView), and
as! is used to force typecasts. If you use
as! and you're wrong, your code will crash.
let submitButton = vw.viewWithTag(10) as! UIButton
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