src/main/java/com/google/devtools/build/lib/syntax/ListComprehension.java


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// Copyright 2014 The Bazel Authors. All rights reserved.
//
// Licensed 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 com.google.devtools.build.lib.syntax;

import com.google.devtools.build.lib.syntax.SkylarkList.MutableList;

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

/**
 * Syntax node for lists comprehension expressions.
 *
 */
public final class ListComprehension extends AbstractComprehension {
  private final Expression outputExpression;

  public ListComprehension(Expression outputExpression) {
    super('[', ']', outputExpression);
    this.outputExpression = outputExpression;
  }

  @Override
  String printExpressions() {
    return outputExpression.toString();
  }

  @Override
  OutputCollector createCollector() {
    return new ListOutputCollector();
  }

  /**
   * Helper class that collects the intermediate results of the {@code ListComprehension} and
   * provides access to the resulting {@code List}.
   */
  private final class ListOutputCollector implements OutputCollector {
    private final List<Object> result;

    ListOutputCollector() {
      result = new ArrayList<>();
    }

    @Override
    public void evaluateAndCollect(Environment env) throws EvalException, InterruptedException {
      result.add(outputExpression.eval(env));
    }

    @Override
    public Object getResult(Environment env) throws EvalException {
      return env.isSkylark() ? new MutableList(result, env) : result;
    }
  }
}