How to check for valid method input using the guard keyword
Swift version: 5.1
The guard keyword was introduced in Swift to signal early returns, which is a coding technique that effectively means "make sure all these things are set up before I start doing the real work in my function, others bail out."
For example, if you want to ensure a submit() is only ever run if an existing name property has a value, you would do this:
func submit() {
guard name != nil else { return }
doImportantWork(name)
}This might seem like a job for a regular if statement, and to be fair that's correct – the two are very similar. The advantage with guard, however, is that it makes your intention clear: these values need to be set up correctly before continuing.
The guard keyword is also helpful because it can be used to check and unwrap optionals that remain unwrapped until the end of the method. For example:
func betterSubmit() {
guard let unwrappedName = name else { return }
doImportantWork(unwrappedName)
}So, if name is nil the method will return; otherwise, it will be safely unwrapped into unwrappedName.
SPONSORED Catch bugs as soon as they happen and know exactly why a crash occurred by integrating Instabug's SDK in one minute. You will automatically receive device data, network logs, and reproduction steps with every bug and crash report.
Sponsor Hacking with Swift and reach the world's largest Swift community!
Available from iOS 7.0
Similar solutions…
- How to detect keyboard input using pressesBegan() and pressesEnded()
- How to do conditional test tear down using addTeardownBlock()
- How to add peek and pop to a UITableView
- How to write performance tests using measure()
- How to test asynchronous functions using expectation()
About the Swift Knowledge Base
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.
