Guard Early Return

Use guard statements for precondition checks and early exits. This keeps the happy path at the lowest indentation level.

// Good — flat, readable
func processOrder(_ order: Order?) {
    guard let order else { return }
    guard order.isValid else {
        log("Invalid order: \(order.id)")
        return
    }
    submitOrder(order)
}

// Bad — nested pyramid
func processOrder(_ order: Order?) {
    if let order = order {
        if order.isValid {
            submitOrder(order)
        }
    }
}

Reserve if let for branches where both the nil and non-nil paths have meaningful work.