TotalMap.scala

object map {
  /**
    * Allows a Map to become total forever.
    * It's isomorphic to `Map.withDefaultValue`, but has a more specific return type, in particular:
    * <ul>
    * <li>it leaves out the information that the returned value is a Map</li>
    * <li>it manifests that the returned value is a total function.</li>
    * </ul>
    *
    * This is useful for a single reason - Maps by default aren't total functions, so `map.apply` can potentially
    * throw an exception. To make working with maps easier, a standard library function exists,
    * namely `withDefaultValue`, that allows the caller to provide a default value that'll be used
    * whenever `apply` is called with a key not recognized by the map.
    * <br/><br/>
    *
    * There's a significant reason why you wouldn't want to use `withDefaultValue` instead - any transformation you apply
    * on it (map, filter, flatMap, etc.) will render `withDefaultValue` useless - the default value will never be used,
    * and the resulting Map's `apply` method can legally throw an exception.
    */
  implicit class TotalMap[K, V](val map: Map[K, V]) extends AnyVal {
    def totalWithDefault[V1 >: V](default: V1): K => V1 = map.getOrElse(_, default)
  }
}