NEW: Subscribe to Hacking with Swift+ and accelerate your learning! >>

Running throwing functions

Swift doesn’t like errors to happen when your program runs, which means it won’t let you run an error-throwing function by accident.

Instead, you need to call these functions using three new keywords: do starts a section of code that might cause problems, try is used before every function that might throw an error, and catch lets you handle errors gracefully.

If any errors are thrown inside the do block, execution immediately jumps to the catch block. Let’s try calling checkPassword() with a parameter that throws an error:

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

When that code runs, “You can’t use that password” is printed, but “That password is good” won’t be – that code will never be reached, because the error is thrown.

Subscribe to Hacking with Swift+

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

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: 4.1/5

Link copied to your pasteboard.