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.calcite.runtime;
  
  import org.checkerframework.checker.nullness.qual.NonNull;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.List;
  import java.util.Map;
  
  import static com.google.common.base.Preconditions.checkArgument;
  
  import static org.apache.calcite.linq4j.Nullness.castNonNull;
  
  import static java.util.Objects.requireNonNull;
  
  /** Immutable list of pairs.
   *
   * @param <T> First type
   * @param <U> Second type
   */
  public interface ImmutablePairList<T, U> extends PairList<T, U> {
  
    /** Creates an empty ImmutablePairList. */
    @SuppressWarnings("unchecked")
    static <T, U> ImmutablePairList<T, U> of() {
      return (ImmutablePairList<T, U>) PairLists.EMPTY;
    }
  
    /** Creates a singleton ImmutablePairList. */
    static <T, U> ImmutablePairList<T, U> of(T t, U u) {
      return new PairLists.SingletonImmutablePairList<>(t, u);
    }
  
    /** Creates an ImmutablePairList with one or more entries. */
    static <T, U> PairList<T, U> copyOf(T t, U u, Object... rest) {
      checkArgument(rest.length % 2 == 0, "even number");
      if (rest.length == 0) {
        return new PairLists.SingletonImmutablePairList<>(t, u);
      }
      Object[] elements = new Object[rest.length + 2];
      elements[0] = requireNonNull(t, "t");
      elements[1] = requireNonNull(u, "u");
      System.arraycopy(rest, 0, elements, 2, rest.length);
      return new PairLists.ArrayImmutablePairList<>(elements);
    }
  
    /** Creates an ImmutablePairList whose contents are a copy of a given
     * collection. */
    @SuppressWarnings("unchecked")
    static <@NonNull T, @NonNull U> ImmutablePairList<T, U> copyOf(
        Iterable<? extends Map.Entry<T, U>> iterable) {
      // Every PairList - mutable and immutable - knows how to quickly make
      // itself immutable.
      if (iterable instanceof PairList) {
        return ((PairList<T, U>) iterable).immutable();
      }
  
      // If it's a collection, we know its size, and therefore can create an
      // array directly, without an intermediate ArrayList.
      if (iterable instanceof Collection) {
        final Collection<? extends Map.Entry<T, U>> collection =
            (Collection<? extends Map.Entry<T, U>>) iterable;
        switch (collection.size()) {
        case 0:
          return of();
  
        case 1:
          // Use of iterator is suboptimal. If we knew this was a list we could
          // call get(0), but the special case doesn't seem worth the effort.
          final Map.Entry<T, U> entry = iterable.iterator().next();
          return of(entry.getKey(), entry.getValue());
  
        default:
          Object[] elements = new Object[2 * collection.size()];
          int i = 0;
          for (Map.Entry<T, U> entry2 : iterable) {
            elements[i++] = castNonNull(entry2.getKey());
            elements[i++] = castNonNull(entry2.getValue());
          }
          return new PairLists.ArrayImmutablePairList<>(elements);
        }
      }
  
      // Not a collection, so we don't know its size in advance.
      final List<Object> list = new ArrayList<>();
      iterable.forEach(entry -> {
        list.add(castNonNull(entry.getKey()));
        list.add(castNonNull(entry.getValue()));
      });
      return PairLists.immutableBackedBy(list);
    }
  
    @Override default ImmutablePairList<T, U> immutable() {
      return this;
    }
  
    @Override ImmutablePairList<T, U> subList(int fromIndex, int toIndex);
  }
  