Error handling isn't usually the most fun part of programming, but as you can see, there can absolutely be some interesting design strategies around it. It is also absolutely critical in developing quality software. We like to think that our users will never run into any problems or unforeseen scenarios, but you might be amazed at how often that happens. We want to do the very best we can to make those scenarios work well, because users will form lasting negative impressions of your product if they get bogged down in unavoidable error situations.
We saw that Swift provides us with a paradigm to help with this called error handling. Functions and methods can be marked as possibly throwing errors and then we can throw any type that implements the ErrorType protocol. We can handle those thrown errors in different ways. We can assert that an error will never be thrown using the try! keyword, we can convert a throwing function or method into an optional with the try? keyword, or we can...