NEW! Master Swift design patterns with my latest book! >>

How to delay execution of code using the defer keyword

Paul Hudson       @twostraws

The defer keyword is new in Swift 2 and lets you schedule some code to be run at a later date. That later date is when your code exits its current scope, which might be when a function returns or at the end of a loop, for example.

If you've used other programming languages, defer will seem similar to try/finally. Any code you defer will run no matter what, even if you throw an exception.

In the example code below, the closeFile() function will get called no matter how the writeLog() function ends:

func writeLog() {
    let file = openFile()
    defer { closeFile(file) }

    let hardwareStatus = fetchHardwareStatus()
    guard hardwareStatus != "disaster" else { return }
    file.write(hardwareStatus)

    let softwareStatus = fetchSoftwareStatus()
    guard softwareStatus != "disaster" else { return }
    file.write(softwareStatus)

    let networkStatus = fetchNetworkStatus()
    guard networkStatus != "disaster" else { return }
    file.write(networkStatus)
}

Available from iOS 7.0

Did this solution work for you? Please pass it on!

Other people are reading…

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.

Get six books for only $150

The Swift Power Pack includes my first six books for one low price, helping you jumpstart a new career in iOS development – check it out!

MASTER SWIFT NOW
Buy Practical iOS 12 Buy Pro Swift Buy Swift Design Patterns Buy Practical iOS 11 Buy Swift Coding Challenges Buy Server-Side Swift (Vapor Edition) Buy Server-Side Swift (Kitura Edition) Buy Hacking with macOS Buy Advanced iOS Volume One Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with Swift Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Beyond Code

Was this page useful? Let me know!

Click here to visit the Hacking with Swift store >>