getOrElse

GetOrElse is a method used in functional programming to provide a fallback value when a value is missing. In the Scala standard library, getOrElse is defined on the Option[T] type and is commonly used to handle optional values without throwing exceptions.

For an Option[A], the signature is def getOrElse[B >: A](or: => B): B. The method returns the contained value when the option is Some(a). If the option is None, it evaluates the argument or and returns that default value. The or parameter is by-name, meaning the default is computed lazily and only if needed.

Examples illustrate its typical use. val x: Option[Int] = Some(3); x.getOrElse(0) yields 3. val y: Option[Int] = None; y.getOrElse(0) yields 0. A lazy default can be provided to avoid unnecessary work, such as val s: Option[String] = None; s.getOrElse { computeDefault() } where computeDefault() is invoked only when the option is None.

Relation to other constructs: getOrElse complements map and flatMap for transforming options, and pairs with orElse and fold to supply defaults in broader control flow. It is a common pattern in Scala and appears in similar forms in other languages’ optional/maybe types (for example, Optional.orElse in Java, or Maybe with a default in functional libraries).

Notes: The by-name default enables lazy evaluation, which is important when the default is expensive to compute or has side effects. The method also enforces type compatibility through its type parameter B >: A.