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.rex;
  
  import org.apache.calcite.rel.core.CorrelationId;
  import org.apache.calcite.rel.type.RelDataType;
  import org.apache.calcite.sql.SqlKind;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.Objects;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * Reference to the current row of a correlating relational expression.
   *
   * <p>Correlating variables are introduced when performing nested loop joins.
   * Each row is received from one side of the join, a correlating variable is
   * assigned a value, and the other side of the join is restarted.
   */
  public class RexCorrelVariable extends RexVariable {
    public final CorrelationId id;
  
    //~ Constructors -----------------------------------------------------------
  
    RexCorrelVariable(
        CorrelationId id,
        RelDataType type) {
      super(id.getName(), type);
      this.id = requireNonNull(id, "id");
    }
  
    //~ Methods ----------------------------------------------------------------
  
    @Override public <R> R accept(RexVisitor<R> visitor) {
      return visitor.visitCorrelVariable(this);
    }
  
    @Override public <R, P> R accept(RexBiVisitor<R, P> visitor, P arg) {
      return visitor.visitCorrelVariable(this, arg);
    }
  
    @Override public SqlKind getKind() {
      return SqlKind.CORREL_VARIABLE;
    }
  
    @Override public boolean equals(@Nullable Object obj) {
      return this == obj
          || obj instanceof RexCorrelVariable
          && Objects.equals(digest, ((RexCorrelVariable) obj).digest)
          && type.equals(((RexCorrelVariable) obj).type)
          && id.equals(((RexCorrelVariable) obj).id);
    }
  
    @Override public int hashCode() {
      return Objects.hash(digest, type, id);
    }
  }
  