Handling try and throws in Swift 3

Question

Before Swift 3 I was using:

guard let data = Data(contentsOf: url) else {
                print("There was an error!)
                return
            }

However I now have to use do, try and catch. I'm not familiar with this syntax. How would I replicate this behaviour?

score 109 · Accepted Answer · answered Sep 28 '16 at 15:46

109

The difference here is that Data(contentsOf: url) does not return an Optional anymore, it throws.

So you can use it in Do-Catch but without guard:

do {
    let data = try Data(contentsOf: url)
    // do something with data
    // if the call fails, the catch block is executed
} catch {
    print(error.localizedDescription)
}

Note that you could still use guard with try? instead of try but then the possible error message is ignored. In this case, you don't need a Do-Catch block:

guard let data = try? Data(contentsOf: url) else {
    print("There was an error!")
    // return or break
}
// do something with data

answered Sep 28 '16 at 15:46

Eric Aya

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2

Thanks for this! The second example is exactly what I'm looking for! – KexAri Sep 28 '16 at 16:11
2

@Moritz Is there a way to add the error message to the else clause? – Sentry.co Aug 27 '17 at 14:43
1

@GitSync Not with `try?`, no. You need Do-Try-Catch to get the error message. – Eric Aya Aug 27 '17 at 14:45
1

@Moritz Thanks for the simple answer – Sean Oct 06 '17 at 09:36

Handling try and throws in Swift 3

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