Simple in-memory cache in Scala

EternalInMemoryCache.scala

import java.util.concurrent.ConcurrentHashMap
class EternalInMemoryCache[A, B]{
  private val underlying = new ConcurrentHashMap[A,B]()
  def cached(key: A)(value: => B): B = {
    Option(underlying.get(key)) match {
      case Some(v) => v
      case None =>
        underlying.put(key, value)
        value
    }
  }
}
val cache = new EternalInMemoryCache[String, String]
cache.cached("foo"){"bar"}