content: /*
   * 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.beam.sdk.coders;
  
  import java.util.List;
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /**
   * An abstract base class to implement a {@link Coder} that defines equality, hashing, and printing
   * via the class name and recursively using {@link #getComponents}.
   *
   * <p>A {@link StructuredCoder} should be defined purely in terms of its component coders, and
   * contain no additional configuration.
   *
   * <p>To extend {@link StructuredCoder}, override the following methods as appropriate:
   *
   * <ul>
   *   <li>{@link #getComponents}: the default implementation returns {@link #getCoderArguments}.
   *   <li>{@link #getEncodedElementByteSize} and {@link #isRegisterByteSizeObserverCheap}: the
   *       default implementation encodes values to bytes and counts the bytes, which is considered
   *       expensive. The default element byte size observer uses the value returned by {@link
   *       #getEncodedElementByteSize}.
   * </ul>
   */
  public abstract class StructuredCoder<T> extends Coder<T> {
    protected StructuredCoder() {}
  
    /**
     * Returns the list of {@link Coder Coders} that are components of this {@link Coder}.
     *
     * <p>The default components will be equal to the value returned by {@link #getCoderArguments()}.
     */
    public List<? extends Coder<?>> getComponents() {
      return getCoderArguments();
    }
  
    /**
     * {@inheritDoc}
     *
     * @return {@code true} if the two {@link StructuredCoder} instances have the same class and equal
     *     components.
     */
    @Override
    public boolean equals(@Nullable Object o) {
      if (o == null || this.getClass() != o.getClass()) {
        return false;
      }
      StructuredCoder<?> that = (StructuredCoder<?>) o;
      return this.getComponents().equals(that.getComponents());
    }
  
    @Override
    public int hashCode() {
      return getClass().hashCode() * 31 + getComponents().hashCode();
    }
  
    @Override
    public String toString() {
      StringBuilder builder = new StringBuilder();
      String s = getClass().getName();
      builder.append(s.substring(s.lastIndexOf('.') + 1));
  
      List<? extends Coder<?>> componentCoders = getComponents();
      if (!componentCoders.isEmpty()) {
        builder.append('(');
        boolean first = true;
        for (Coder<?> componentCoder : componentCoders) {
          if (first) {
            first = false;
          } else {
            builder.append(',');
          }
          builder.append(componentCoder.toString());
        }
        builder.append(')');
      }
      return builder.toString();
    }
  }
  