Today while reviewing code of my colleague I came across of this:

private func signedValueText(_ value: Int) -> String {
    let sign = value > 0 ? "+" : ""
    return sign + String(value)

Read Secrets of printf:

In the most simple case, printf takes one argument: a string of characters to be printed. This string is composed of characters, each of which is printed exactly as it appears. So printf("xyz"); would simply print an “x”, then a “y”, and finally a “z”. This is not exactly “formatted” printing, but it is still the basis of what printf does.