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.