I'm reading the officital Swift documents "The Swift Programming language (Swift 2.2)". In the topics of Optionals under the Baseics section
I found the following descriptions which has somthing to do with initializer.
"The example below uses the initializer to try to convert a String into an Int:
let possibleNumber = "123"
let convertedNumber = Int(possibleNumber)
convertedNumber is an Object.
Int(...) actually initialize the
convertedNumber Object for you. As conversion
Int is not guaranteed to success,
convertedNumber is optional.