In Swift 3, when one has optional function parameters, what is the difference between functions with:
func doThis(num: Int!)
and
func doThat(num: Int?)
Both declare that num is an optional Int.
If you do Int! it can be implicitly unwrapped inside of your function. That means you can use it in places where a plain (non-optional) Int is required. In that case, it will fail if it happens to be nil.
With a "proper" Int? the compiler will not let you use num where an Int is required and forces you to include a check/guard first.
The Int! construct is mostly there for interoperability with Objective-C code where it is not clear if a reference type is optional or not. You should avoid it in new code.
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