Guard for early exit pattern in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the guard statement in Swift?

The guard statement checks a condition and exits the current scope early if the condition is not met. It helps keep the main code path clear and avoids deep nesting.

beginner

How does the guard statement improve code readability?

By handling error or invalid cases early and exiting, guard keeps the main logic at the top level without extra indentation, making the code easier to read and understand.

intermediate

What must happen inside the else block of a guard statement?

The else block must exit the current scope using return, break, continue, or throw. This ensures the program does not continue if the condition fails.

beginner

Example: What will this code print?<br><pre>func checkAge(_ age: Int?) {
 guard let age = age, age >= 18 else {
   print("Not allowed")
   return
 }
 print("Allowed")
}
checkAge(20)
checkAge(15)
checkAge(nil)</pre>

The code prints:<br>Allowed for 20 because age is valid and >= 18.<br>Not allowed for 15 because age is less than 18.<br>Not allowed for nil because age is missing.

intermediate

Why is guard preferred over nested if statements for early exit?

guard reduces nested code blocks by exiting early when conditions fail. This leads to cleaner, flatter code that is easier to follow and maintain.

What must the else block of a guard statement do?

A Exit the current scope with return, break, continue, or throw

B Do nothing and continue execution

C Only print an error message

D Declare new variables

The else block must exit the current scope to prevent continuing when the guard condition fails.

Which keyword is used in Swift to check a condition and exit early if it fails?

A guard

B if

C switch

D while

guard is designed for early exit when a condition is not met.

What happens if the guard condition is true?

A The code inside <code>else</code> runs

B The program exits immediately

C Execution continues after the guard statement

D The program crashes

If the guard condition is true, the program continues normally after the guard statement.

Why is guard useful for unwrapping optionals?

A It forces the optional to be nil

B It unwraps the optional and exits early if nil

C It converts optionals to strings

D It ignores optionals

guard let unwraps optionals and exits early if the value is nil, avoiding crashes.

Which of these is NOT a valid way to exit inside a guard else block?

A return

B break

C continue

D print("Error")

Simply printing an error does not exit the scope; you must use return, break, continue, or throw.

Explain how the guard statement helps with early exit in Swift functions.

Think about how guard checks conditions and what happens if they fail.

Describe a real-life example where using guard for early exit makes code easier to read.

Imagine checking if a user input is valid before continuing.