Swift's guard keyword

Question

Swift 2 introduced the guard keyword, which could be used to ensure that various data is configured ready to go. An example I saw on this website demonstrates a

Answer 1

From Apple documentation:

Guard Statement

A guard statement is used to transfer program control out of a scope if one or more conditions aren’t met.

Synatx:

guard condition else {
    statements
}

Advantage:

1. By using guard statement we can get rid of deeply nested conditionals whose sole purpose is validating a set of requirements.

2. It was designed specifically for exiting a method or function early.

if you use if let below is the code how it looks.

  let task = URLSession.shared.dataTask(with: request) { (data, response, error) in

        if error == nil {
            if let  statusCode = (response as? HTTPURLResponse)?.statusCode, statusCode >= 200 && statusCode <= 299 {
                if let data = data {

                    //Process Data Here.
                    print("Data: \(data)")

                } else {
                    print("No data was returned by the request!")
                }
            } else {
                print("Your request returned a status code other than 2XX!")
            }
        } else {
            print("Error Info: \(error.debugDescription)")
        }
    }
    task.resume()

Using guard you can transfer control out of a scope if one or more conditions aren't met.

let task = URLSession.shared.dataTask(with: request) { (data, response, error) in

            /* GUARD: was there an error? */
            guard (error == nil) else {
                print("There was an error with your request: \(error)")
                return
            }

            /* GUARD: Did we get a successful 2XX response? */
            guard let statusCode = (response as? HTTPURLResponse)?.statusCode, statusCode >= 200 && statusCode <= 299 else {
                print("Your request returned a status code other than 2XX!")
                return
            }

            /* GUARD: was there any data returned? */
            guard let data = data else {
                print("No data was returned by the request!")
                return
            }

            //Process Data Here.
            print("Data: \(data)")
}
task.resume()

Reference:

1. Swift 2: Exit Early With guard 2. Udacity 3. Guard Statement