Swift 4 Protocol-Oriented Programming - Third Edition

Text validation

In numerous apps, across multiple platforms (iOS, Android, and Windows), I have been tasked to validate user input either after the user has entered it or as it is entered. This validation can be done very easily with regular expressions; however, we do not want various regular expression strings littered throughout our code. We can solve this problem by creating different classes or structures that contain the validation code. The question is; how would we organize these types to make them easy to use and maintain? Prior to protocol extensions in Swift, I would have used protocols to define the validation requirements and would then create a type that conforms to the protocol for each validation type needed.

Prior to looking ...