Scala mutable MultiMap addBinding 和插入顺序保存

Question

MultiMap 的 addBinding 似乎不保留绑定(bind)到同一键的值的插入顺序，因为它使用的底层机制是 HashSet。使用 MultiMap 保留插入顺序的惯用方法是什么？

Answer 1

基于 MultiMap其中实现说明:

/** Creates a new set.
*
*  Classes that use this trait as a mixin can override this method
*  to have the desired implementation of sets assigned to new keys.
*  By default this is `HashSet`.
*
*  @return An empty set of values of type `B`.
*/
protected def makeSet: Set[B] = new HashSet[B]

您可以简单地定义:

trait OrderedMultimap[A, B] extends MultiMap[A, B] {
    override def makeSet: Set[B] = new LinkedHashSet[B]
}