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

The ! at the end of an object says the object is an optional and to unwrap if it can otherwise returns a nil. This is often used to trap errors that would otherwise crash the program.