code block for README-27

README-27

// Nullable constructor arg w/default
class Numberer(pattern: String? = null) {

  companion object {
    // Public constant
    const val DEF_PATTERN = "000,000"
  }

  // Private field w/fallback value (?:)
  private val formatter =
    DecimalFormat(pattern ?: DEF_PATTERN)

  fun numberLines(lines: List<String>) =
    // lines.indices: 0 until lines.size
    lines.indices.map { index ->
      formatter.format(index + 1) +
        " " + lines[index]
    }
}

fun main() {
    val numberer = Numberer("00")
    val words = listOf(
        "out", "of", "mind",
        "back", "in", "five"
    )
    // lambda w/method reference
    numberer.numberLines(words)
        .forEach(::println)
    /*
       prints:
         01 out
         02 of
         03 mind
         04 back
         05 in
         06 five
    */
}