The guard Statement

func name(param: Type) {
    guard condition else {
        // must exit: return, break, continue or throw
        return
    }
    // continue when condition is true
}

// Define the function `describe` taking `age`
func describe(age: Int) {
    guard age >= 0 else {
        // Print "Invalid age" to the console
        print("Invalid age")
        return
    }
    // Print "Age is \(age)" to the console
    print("Age is \(age)")
}
describe(age: 25)
describe(age: -5)

// Define the function `processScore` taking `score`
func processScore(_ score: Int) {
    guard score >= 0, score <= 100 else {
        // Print "Score out of range" to the console
        print("Score out of range")
        return
    }
    // Print "Valid score: \(score)" to the console
    print("Valid score: \(score)")
}
processScore(150)
processScore(85)

Switch Statement Basics · guard let Unwrapping · The defer Statement · If-Else Statements

1. Forgetting that a guard block's else clause MUST exit the current scope (via return, break, continue, or throw) -- Swift enforces this at compile time.
2. Using guard for the main happy-path logic instead of for validating and exiting early; guard is meant for early exits, if for branching.
3. Not realizing that variables bound in guard let remain available for the REST of the enclosing scope, unlike an if let binding which is scoped to its own block.

• guard checks a condition and requires an else block that exits scope if the condition fails.
• It's typically used for early-exit validation at the top of a function.
• Values unwrapped via guard let remain usable for the rest of the function, improving readability over nested if let.
• The Swift compiler enforces that the else branch of a guard must leave the current scope.