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@Evolving
public class QueryResult<R> {
  // wraps a successful result
  public static <R> QueryResult<R> forResult(R result);

  // returns a failed query result because the store didn't know how to handle the query.
  public static <R> QueryResult<R> forUnknownQueryType(Query<R> query, StateStore store);

  // returns a failed query result because the partition wasn't caught up to the desired bound.
  public static <R> QueryResult<R> notUpToBound(Position currentPosition, Position bound);

  // returns a failed query result because caller requested a "latest" bound, but the task was
  // not active and running.
  public static <R> QueryResult<R> notActive(String currentState);

  // Used by state stores that need to delegate to another store to run a query and then
  // translate the results. Does not change the execution info or any other metadata.
  public <NewR> QueryResult<NewR> swapResult(NewR newTypedResult);

  // If requested, stores should record
  // helpful information, such as their own class, how they executed the query,
  // and the time they took.
  public void addExecutionInfo(String executionInfo);

  public boolean isSuccess();
  public boolean isFailure();
  public List<String> getExecutionInfo();
  public FailureReason getFailureReason();
  public String getFailure();
}