DAY 14

Optionals

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Null references – literally when a variable has no value – were invented by Tony Hoare way back in 1965. When asked about it in retrospect, he said “I call it my billion-dollar mistake” because they lead to so many problems.

This is the last day that you’ll be learning the fundamentals of Swift, and it’s devoted exclusively to Swift’s solution to null references, known as optionals. These are a really important language feature, but they can hurt your brain a little – don’t feel bad if you need to repeat some tutorials a few times.

In essence, an optional is trying to answer the question “what if our variable doesn’t have any sort of value at all?” Swift wants to make sure all our programs are as safe as possible, so it has some very specific – and very important! – techniques for handling this eventuality.

Today you have five tutorials to work through, where you’ll meet optionals, optional unwrapping, nil coalescing, and more. Once you’ve watched each video and optionally gone through the extra reading, there are short tests to help make sure you’ve understood what was taught.

Tip: Yes, there is optional reading about optionals, but these optionals aren’t empty!

1. How to handle missing data with optionals
   • Optional: Why does Swift have optionals?
   • Optional: Why does Swift make us unwrap optionals?
   • Test: Unwrapping optionals
2. How to unwrap optionals with guard
   • Optional: When to use guard let rather than if let
   • Test: Unwrapping with guard
3. How to unwrap optionals with nil coalescing
   • Optional: When should you use nil coalescing in Swift?
   • Test: Nil coalescing
4. How to handle multiple optionals using optional chaining
   • Optional: Why is optional chaining so important?
   • Test: Optional chaining
5. How to handle function failure with optionals
   • Optional: When should you use optional try?
   • Test: Optional try
6. Summary: Optionals
7. Checkpoint 9

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