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.plan;
  
  import org.apache.calcite.rel.RelDistributions;
  import org.apache.calcite.rel.core.Project;
  import org.apache.calcite.util.mapping.Mappings;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /**
   * RelTrait represents the manifestation of a relational expression trait within
   * a trait definition. For example, a {@code CallingConvention.JAVA} is a trait
   * of the {@link ConventionTraitDef} trait definition.
   *
   * <h2><a id="EqualsHashCodeNote">Note about equals() and hashCode()</a></h2>
   *
   * <p>If all instances of RelTrait for a particular RelTraitDef are defined in
   * an {@code enum} and no new RelTraits can be introduced at runtime, you need
   * not override {@link #hashCode()} and {@link #equals(Object)}. If, however,
   * new RelTrait instances are generated at runtime (e.g. based on state external
   * to the planner), you must implement {@link #hashCode()} and
   * {@link #equals(Object)} for proper {@link RelTraitDef#canonize canonization}
   * of your RelTrait objects.
   */
  public interface RelTrait {
    //~ Methods ----------------------------------------------------------------
  
    /**
     * Returns the RelTraitDef that defines this RelTrait.
     *
     * @return the RelTraitDef that defines this RelTrait
     */
    RelTraitDef getTraitDef();
  
    /**
     * See <a href="#EqualsHashCodeNote">note about equals() and hashCode()</a>.
     */
    @Override int hashCode();
  
    /**
     * See <a href="#EqualsHashCodeNote">note about equals() and hashCode()</a>.
     */
    @Override boolean equals(@Nullable Object o);
  
    /**
     * Returns whether this trait satisfies a given trait.
     *
     * <p>A trait satisfies another if it is the same or stricter. For example,
     * {@code ORDER BY x, y} satisfies {@code ORDER BY x}.
     *
     * <p>A trait's {@code satisfies} relation must be a partial order (reflexive,
     * anti-symmetric, transitive). Many traits cannot be "loosened"; their
     * {@code satisfies} is an equivalence relation, where only X satisfies X.
     *
     * <p>If a trait has multiple values
     * (see {@link org.apache.calcite.plan.RelCompositeTrait})
     * a collection (T0, T1, ...) satisfies T if any Ti satisfies T.
     *
     * @param trait Given trait
     * @return Whether this trait subsumes a given trait
     */
    boolean satisfies(RelTrait trait);
  
    /**
     * Returns a succinct name for this trait. The planner may use this String
     * to describe the trait.
     */
    @Override String toString();
  
    /**
     * Registers a trait instance with the planner.
     *
     * <p>This is an opportunity to add rules that relate to that trait. However,
     * typical implementations will do nothing.
     *
     * @param planner Planner
     */
    void register(RelOptPlanner planner);
  
    /**
     * Applies a mapping to this trait.
     *
     * <p>Some traits may be changed if the columns order is changed by a mapping
     * of the {@link Project} operator.
     *
     * <p>For example, if relation {@code SELECT a, b ORDER BY a, b} is sorted by
     * columns [0, 1], then the project {@code SELECT b, a} over this relation
     * will be sorted by columns [1, 0]. In the same time project {@code SELECT b}
     * will not be sorted at all because it doesn't contain the collation
     * prefix and this method will return an empty collation.
     *
     * <p>Other traits are independent from the columns remapping. For example
     * {@link Convention} or {@link RelDistributions#SINGLETON}.
     *
     * @param mapping   Mapping
     * @return trait with mapping applied
     */
    default <T extends RelTrait> T apply(Mappings.TargetMapping mapping) {
      return (T) this;
    }
  
    /**
     * Returns whether this trait is the default trait value.
     */
    default boolean isDefault() {
      return this == getTraitDef().getDefault();
    }
  }
  