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Why is optional chaining so important?

Paul Hudson    @twostraws   

Updated for Xcode 14.2

Swift’s optional chaining lets us dig through several layers of optionals in a single line of code, and if any one of those layers is nil then the whole line becomes nil.

As a simple example, we might have a list of names and want to find where they should be placed based on the first letter of their surname:

let names = ["Vincent": "van Gogh", "Pablo": "Picasso", "Claude": "Monet"]
let surnameLetter = names["Vincent"]?.first?.uppercased()

There we use optional chaining with the dictionary value because names["Vincent"] might not exist, and again when reading the first character from the surname, because it’s possible the string could be empty.

Optional chaining makes for a very good companion to nil coalescing, because it allows you to dig through layers of optionals while also providing a sensible fall back if any of the optionals are nil.

Returning to our surname example, we could automatically return “?” if we were unable to read the first letter of someone’s surname:

let surnameLetter = names["Vincent"]?.first?.uppercased() ?? "?"

For more information on optional chaining, I can recommend this blog post from Andy Bargh:

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