core/src/main/java/org/apache/calcite/util/Static.java

/*
 * 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.util;

import org.apache.calcite.runtime.CalciteResource;
import org.apache.calcite.runtime.ConsList;
import org.apache.calcite.runtime.Resources;

import java.util.List;

/**
 * Definitions of objects to be statically imported.
 *
 * <h2>Note to developers</h2>
 *
 * <p>Please give careful consideration before including an object in this
 * class. Pros:
 * <ul>
 * <li>Code that uses these objects will be terser.
 * </ul>
 *
 * <p>Cons:</p>
 * <ul>
 * <li>Namespace pollution,
 * <li>code that is difficult to understand (a general problem with static
 * imports),
 * <li>potential cyclic initialization.
 * </ul>
 */
public abstract class Static {
  private Static() {}

  /** Resources. */
  public static final CalciteResource RESOURCE =
      Resources.create(CalciteResource.class);

  /** Builds a list. */
  public static <E> List<E> cons(E first, List<? extends E> rest) {
    return ConsList.of(first, rest);
  }
}