SALE: Save 50% on all my books and bundles >>

Optional try

Back when we were talking about throwing functions, we looked at this code:

enum PasswordError: Error {
    case obvious
}

func checkPassword(_ password: String) throws -> Bool {
    if password == "password" {
        throw PasswordError.obvious
    }

    return true
}

do {
    try checkPassword("password")
    print("That password is good!")
} catch {
    print("You can't use that password.")
}

That runs a throwing function, using do, try, and catch to handle errors gracefully.

There are two alternatives to try, both of which will make more sense now that you understand optionals and force unwrapping.

The first is try?, and changes throwing functions into functions that return an optional. If the function throws an error you’ll be sent nil as the result, otherwise you’ll get the return value wrapped as an optional.

Using try? we can run checkPassword() like this:

if let result = try? checkPassword("password") {
    print("Result was \(result)")
} else {
    print("D'oh.")
}

The other alternative is try!, which you can use when you know for sure that the function will not fail. If the function does throw an error, your code will crash.

Using try! we can rewrite the code to this:

try! checkPassword("sekrit")
print("OK!")
Hacking with Swift is sponsored by RevenueCat

SPONSORED Building in-app subscriptions are hard – especially cross-platform. RevenueCat makes it simple. With their native SDKs, you can implement a custom subscription model for your app in hours, not months.

Explore the docs to learn more

Sponsor Hacking with Swift and reach the world's largest Swift community!

Cascable unleashes the power of your camera and unlocks powerful workflows for shooting, managing, and geotagging your photos.

BUY OUR BOOKS
Buy Pro Swift Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift (Vapor Edition) Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Server-Side Swift (Kitura Edition) Buy Beyond Code

Was this page useful? Let us know!

Average rating: 4.5/5