Swift 2 introduced the guard keyword, a handy bit of syntactic sugar with semantics similar to a debugging assert. It’s pure sugar, nothing more than an alternate if construction, but I’ve found that liberal use of guard has made my code far more readable with very little effort.
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func checkAuthenticated(authenticated: Bool) -> Bool {
guard authenticated else {
// Do something in response to failure
return false
}
return true
}
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Basically, guard is a sort of inverse if. You could just as easily write the (hilariously contrived) above example as:
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func checkAuthenticated(authenticated: Bool) -> Bool {
if !authenticated {
// Do something in response to failure
return false
}
return true
}
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I strongly prefer the guard version, though, as I find the guard...else line to be much more explicit than the narrow and easily-overlooked !. guard really comes into its own, however, when dealing with optionals. I often find that I end up with a lot of code like:
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func updateGameCenterDisplay(username: String?) {
if let user = username {
// Do something sensible with ‘user’.
usernameLabel.text = user
return
}
// username is nil, prompt for login.
}
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This is fine, but it feels like inverted logic. I’d far rather take care of the error cases up front, and guard lets me do just that:
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func updateGameCenterDisplay(username: String?) {
guard let user = username else {
// username is nil, prompt for login.
return
}
// Do something sensible with ‘user’.
usernameLabel.text = user
}
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