Functions and optional results

The idea

An optional such as Int? contains either a value or nil. It describes absence in the type rather than encoding it as an ordinary number that could be valid data. Converting text with Int(...) returns an optional because the text might not be a valid integer. A function signature should make that possibility visible to its callers.

Optional binding with if let or guard let introduces a usable nonoptional value only in the successful path. The nil-coalescing operator ?? supplies a fallback when no value is present. Forced unwrapping with ! should not be a substitute for understanding the input. When failure is expected, choose an explicit branch that can explain or recover from it.

func nextCount(_ text: String) -> Int? {
    guard let value = Int(text) else { return nil }
    return value + 1
}
print(nextCount("8") ?? -1)
print(nextCount("eight") ?? -1)

9
-1

Valid numeric text is unwrapped and incremented. Invalid text returns nil, so the caller chooses its explicit fallback.