As many of you know, I am converting one of my apps from Obj-C to Swift. It's called Quit That! and tracks things you want to quit. The date you quit is very important and several different calculations are based on it. I ran across this post in my googling and found it to be very helpful and straightforward in deciphering how to convert a date String to Date. As a side note, I also learned that CoreData only stores NSDate, which is a pain if you want to user Date in your code. I settled on storing the date as a string in CoreData and converting to Date on retrieval.
This was the most important part for me. I couldn't figure out why I kept getting nil!
Be careful with this last step, that one can return nil if the dateFormat doesn’t match with the format of your stringDate
Converting Date String to Date Type with Swift by Luis Arias
There are other options besides Fatal Error. As Dejan explains, many developers differ on how they should be used, so it's up to you to understand the differences.
Sometimes it’s better to crash than to have your app running in an inconsistent state
Assert, Precondition and Fatal Error in Swift by Dejan Agostini