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Create a well-defined, cross-language specification for data compute operations

There is a newer version: 0.46.1

package io.substrait.relation;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.function.Supplier;

/** Provides common utilities for copy-on-write visitations */
public class CopyOnWriteUtils {

  public static boolean allEmpty(Optional... optionals) {
    return Arrays.stream(optionals).noneMatch(Optional::isPresent);
  }

  /** The `or` method on Optional instances is a Java 9+ feature */
  public static  Optional or(Optional left, Supplier> right) {
    if (left.isPresent()) {
      return left;
    } else {
      return right.get();
    }
  }

  @FunctionalInterface
  public interface TransformFunction {
    Optional apply(T t) throws E;
  }

  /**
   * Applies the given transformation function to each item in the list. If any of the list items
   * are transformed, returns a new list in which each item is either
   *
   * 
   *   a transformed new item replacing an old item
   *   
the original item in the position it was in
   * 
   *
   * @param items the list of items to transform
   * @param transform the transformation function to apply to each item
   * @return An empty optional if none of the items have changed. An optional containing a new list
   *     otherwise.
   */
  public static  Optional> transformList(
      List items, TransformFunction transform) throws E {
    List newItems = new ArrayList<>();
    boolean listUpdated = false;
    for (ITEM item : items) {
      Optional newItem = transform.apply(item);
      if (newItem.isPresent()) {
        newItems.add(newItem.get());
        listUpdated = true;
      } else {
        newItems.add(item);
      }
    }
    return listUpdated ? Optional.of(newItems) : Optional.empty();
  }
}