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.linq4j;
  
  import org.apache.calcite.linq4j.tree.Expression;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.lang.reflect.Type;
  import java.util.Iterator;
  
  /**
   * Skeleton implementation of {@link Queryable}.
   *
   * <p>The default implementation of {@link #enumerator()} calls the provider's
   * {@link QueryProvider#executeQuery(Queryable)} method, but the derived class
   * can override.
   *
   * @param <TSource> Element type
   */
  public abstract class BaseQueryable<TSource>
      extends AbstractQueryable<TSource> {
    protected final QueryProvider provider;
    protected final Type elementType;
    protected final @Nullable Expression expression;
  
    protected BaseQueryable(QueryProvider provider, Type elementType,
        @Nullable Expression expression) {
      this.provider = provider;
      this.elementType = elementType;
      this.expression = expression;
    }
  
    @Override public QueryProvider getProvider() {
      return provider;
    }
  
    @Override public Type getElementType() {
      return elementType;
    }
  
    @Override public @Nullable Expression getExpression() {
      return expression;
    }
  
    @Override public Iterator<TSource> iterator() {
      return Linq4j.enumeratorIterator(enumerator());
    }
  
    @Override public Enumerator<TSource> enumerator() {
      return provider.executeQuery(this);
    }
  }
  