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A module that is everything required to understands Druid Segments

There is a newer version: 30.0.1

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.druid.frame.read.columnar;

import org.apache.druid.frame.Frame;
import org.apache.druid.query.rowsandcols.column.Column;
import org.apache.druid.segment.column.RowSignature;

/**
 * Embeds the logic to read a specific column from frames with a specific {@link RowSignature}. Stateless and immutable,
 * so it can be shared between multiple frame readers as long as all frames have the same signature.
 */
public interface FrameColumnReader
{
  /**
   * Returns a {@link Column} from the frame.
   */
  Column readRACColumn(Frame frame);

  /**
   * Returns a column reference for the provided frame.
   */
  ColumnPlus readColumn(Frame frame);
}