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.util.mapping;
  
  import java.util.Iterator;
  
  /**
   * A <dfn>Mapping</dfn> is a relationship between a source domain to target
   * domain of integers.
   *
   * <p>This interface represents the most general possible mapping. Depending on
   * the {@link MappingType} of a particular mapping, some of the operations may
   * not be applicable. If you call the method, you will receive a runtime error.
   * For instance:
   *
   * <ul>
   * <li>If a target has more than one source, then the method
   *     {@link #getSource(int)} will throw
   *     {@link Mappings.TooManyElementsException}.
   * <li>If a source has no targets, then the method {@link #getTarget} will throw
   *     {@link Mappings.NoElementException}.
   * </ul>
   */
  public interface Mapping
      extends Mappings.FunctionMapping,
      Mappings.SourceMapping,
      Mappings.TargetMapping,
      Iterable<IntPair> {
    //~ Methods ----------------------------------------------------------------
  
    /**
     * Returns an iterator over the elements in this mapping.
     *
     * <p>This method is optional; implementations may throw
     * {@link UnsupportedOperationException}.
     */
    @Override Iterator<IntPair> iterator();
  
    /**
     * Returns the number of sources. Valid sources will be in the range 0 ..
     * sourceCount.
     */
    @Override int getSourceCount();
  
    /**
     * Returns the number of targets. Valid targets will be in the range 0 ..
     * targetCount.
     */
    @Override int getTargetCount();
  
    @Override MappingType getMappingType();
  
    /**
     * Returns whether this mapping is the identity.
     */
    @Override boolean isIdentity();
  
    /**
     * Removes all elements in the mapping.
     */
    void clear();
  
    /**
     * Returns the number of elements in the mapping.
     */
    @Override int size();
  }
  