LazyMap ftw

LazyMap.scala

package com.yieldmo.rtb.util

class LazyMap[A,B](delegate: Map[A,() => B]) extends scala.collection.immutable.Map[A,B]{
  def get(key: A): Option[B] = delegate.get(key).map{ _() }
  def iterator: Iterator[(A,B)] = delegate.iterator.map{ pair => (pair._1, pair._2()) }
  def +[B1 >:B](kv: (A, B1)): Map[A, B1] = new LazyMap[A,B1](delegate + (kv._1 -> (() => kv._2)))
  def -(key: A): Map[A, B] = new LazyMap[A,B](delegate - key)
}