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Why does Swift make us use try before every throwing function?

Paul Hudson    @twostraws   

Updated for Xcode 13.2

Using Swift’s throwing functions relies on three unique keywords: do, try, and catch. We need all three to be able to call a throwing function, which is unusual – most other languages use only two, because they don’t need to write try before every throwing function.

The reason Swift is different is fairly simple: by forcing us to use try before every throwing function, we’re explicitly acknowledging which parts of our code can cause errors. This is particularly useful if you have several throwing functions in a single do block, like this:

do {
    try throwingFunction1()
    nonThrowingFunction1()
    try throwingFunction2()
    nonThrowingFunction2()
    try throwingFunction3()
} catch {
    // handle errors
}

As you can see, using try makes it clear that the first, third, and fifth function calls can throw errors, but the second and fourth cannot.

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