Browse Questions
  • The responder chain is a sequence of UIResponder objects that can handle events (touches, key presses, actions).
  • Both safely unwrap optionals, but they differ in scope and intent.
  • Secure Comparator is a zero-knowledge protocol that lets two parties confirm they hold the same secret without either side transmitting it, or leaking anything usable when the secrets differ.
  • Timer and CADisplayLink cause memory leaks because the target-action API causes the active RunLoop to retain the timer, and the timer retains its target object until explicitly invalidated.

Answer: Both safely unwrap optionals, but they differ in scope and intent.

  • if let — unwrapped value exists only inside the if block
  • guard let — unwrapped value exists in the surrounding scope after the check; must exit early if condition fails

Code Example:

// if let — value scoped inside the block
if let username = getUsername() {
    print("Welcome, \(username)")
}
// username not accessible here

// guard let — value available after the guard
func greetUser() {
    guard let username = getUsername() else {
        print("No user")
        return  // must exit
    }
    // username accessible here for the rest of the function
    print("Welcome, \(username)")
}

Rule of thumb: Use guard let for preconditions at the top of a function. Use if let when the unwrapped value is only needed in one branch.