Options and Error Handling

Option Basics

Hold a value that may be missing with Option.

option-basics An `Option[Int]` is either `Some(value)` or `None`. `isDefined` reports whether a value is present, and `getOrElse` supplies a fallback when it is missing.

Option Basics

raw
OptionBasics.scala
Replay: real traced execution (multi-file project)
object Main {
  def main(args: Array[String]): Unit = {
    val raw = 7
    val maybe: Option[Int] = if (raw > 0) Some(raw) else None
    val present = maybe.isDefined
    val value = maybe.getOrElse(0)

    println("present=" + present)
    println("value=" + value)
  }
}

object Main {
  def main(args: Array[String]): Unit = {
    val raw = -3
    val maybe: Option[Int] = if (raw > 0) Some(raw) else None
    val present = maybe.isDefined
    val value = maybe.getOrElse(0)

    println("present=" + present)
    println("value=" + value)
  }
}

object Main {
  def main(args: Array[String]): Unit = {
    val raw = 0
    val maybe: Option[Int] = if (raw > 0) Some(raw) else None
    val present = maybe.isDefined
    val value = maybe.getOrElse(0)

    println("present=" + present)
    println("value=" + value)
  }
}

  1. raw ← 7, maybe ← Some(7), present ← true, maybe.isDefined ← true

    1object Main {2  def main(args: Array[String]): Unit = {3    val raw→ 7 = 7 //@raw=0, -34    val maybe→ Some(7): Option[Int] = if (raw7 > 0) Some(raw) else None5    val present→ true = maybe.isDefined→ true6    val value→ 7 = maybeSome(7).getOrElse(0)78    println("present=" + presenttrue)9    println("value=" + value7)10  }11}
    outputpresent=true
value=7

  1. raw ← -3, maybe ← None, present ← false, maybe.isDefined ← false

    1object Main {2  def main(args: Array[String]): Unit = {3    val raw→ -3 = -34    val maybe→ None: Option[Int] = if (raw-3 > 0) Some(raw) else None5    val present→ false = maybe.isDefined→ false6    val value→ 0 = maybeNone.getOrElse(0)78    println("present=" + presentfalse)9    println("value=" + value0)10  }11}
    outputpresent=false
value=0

  1. raw ← 0, maybe ← None, present ← false, maybe.isDefined ← false

    1object Main {2  def main(args: Array[String]): Unit = {3    val raw→ 0 = 04    val maybe→ None: Option[Int] = if (raw0 > 0) Some(raw) else None5    val present→ false = maybe.isDefined→ false6    val value→ 0 = maybeNone.getOrElse(0)78    println("present=" + presentfalse)9    println("value=" + value0)10  }11}
    outputpresent=false
value=0