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Calcite APIs for LINQ (Language-Integrated Query) in Java

There is a newer version: 1.38.0

/*
 * 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.tree;

import org.checkerframework.checker.nullness.qual.Nullable;

import java.util.ArrayList;
import java.util.List;

/**
 * Holds context for evaluating expressions.
 */
class Evaluator {
  final List parameters = new ArrayList<>();
  final List<@Nullable Object> values = new ArrayList<>();

  Evaluator() {
  }

  void push(ParameterExpression parameter, @Nullable Object value) {
    parameters.add(parameter);
    values.add(value);
  }

  void pop(int n) {
    while (n > 0) {
      parameters.remove(parameters.size() - 1);
      values.remove(values.size() - 1);
      --n;
    }
  }

  @Nullable Object peek(ParameterExpression param) {
    for (int i = parameters.size() - 1; i >= 0; i--) {
      if (parameters.get(i) == param) {
        return values.get(i);
      }
    }
    throw new RuntimeException("parameter " + param + " not on stack");
  }

  @Nullable Object evaluate(Node expression) {
    return ((AbstractNode) expression).evaluate(this);
  }

  void clear() {
    parameters.clear();
    values.clear();
  }
}