What does an exclamation mark mean in the Swift language?

Question

The Swift Programming Language guide has the following example:

class Person {
    let name: String
    init(name: String) { self.name = name }
    var apar         


        

Answer 1

In this case...

var John: Person!

it means, that initially John will have nil value, it will be set and once set will never be nil-led again. Therefore for convenience I can use the easier syntax for accessing an optional var because this is an "Implicitly unwrapped optional"