/// <summary>
/// Expert: If <see cref="GetMergeReaders()"/> reorders document IDs, this method
/// must be overridden to return a mapping from the <i>natural</i> doc ID
/// (the doc ID that would result from a natural merge) to the actual doc
/// ID. This mapping is used to apply deletions that happened during the
/// merge to the new segment.
/// </summary>
public virtual DocMap GetDocMap(MergeState mergeState)
{
return(new DocMapAnonymousInnerClassHelper(this));
}