```// 1 fun calculateHour(h: Int, period: String?)...

# codingconventions

[Ellen Spertus]

// 1
fun calculateHour(h: Int, period: String?): Int =
  period?.let {
    when(it) {
      "am" -> if (h == HOURS_PER_PERIOD) 0 else h
      "pm" -> (h % HOURS_PER_PERIOD) + HOURS_PER_PERIOD
      else -> h // should not happen
    }
  } ?: h
}

// 2
fun calculateHour(h: Int, period: String?): Int =
  if (period == null) {
    h
  } else when (period) {
    "am" -> if (h == HOURS_PER_PERIOD) 0 else h
    "pm" -> (h % HOURS_PER_PERIOD) + HOURS_PER_PERIOD
    else -> h // should not happen
  }
}

[Shawn]

but what if

when (period) {
    null -> h
    <http://Period.AM|Period.AM> -> if (h == HOURS_PER_PERIOD) 0 else h
    <http://Period.PM|Period.PM> -> (h % HOURS_PER_PERIOD) + HOURS_PER_PERIOD
}

[Shawn]

use the type system to your advantage

[Ellen Spertus]

But of course! For some reason it didn’t occur to me that null could be a when value. Thank you.

[Shawn]

to be abundantly clear, my example will only compile if you make Period an enum (or sealed class technically but you probably don’t need one to denote AM/PM)

[Shawn]

if you just do string matching you’ll need an else

[Ellen Spertus]

Of course. Only part of my brain was malfunctioning.

[codeslubber]

The naming is probably suboptimal, it’s not calculating anything, it’s formatting, right?