content: /* 
   * Kodkod -- Copyright (c) 2005-present, Emina Torlak
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this software and associated documentation files (the "Software"), to deal
   * in the Software without restriction, including without limitation the rights
   * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
   * copies of the Software, and to permit persons to whom the Software is
   * furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
   * THE SOFTWARE.
   */
  package kodkod.util.collections;
  
  
  /**
   * An index generator for a set of keys.  An indexer maps each key in its keyset 
   * to a unique integer in the range [0..#keys)
   * @specfield keys: set K
   * @specfield indices: keys lone->one [0..#keys)
   * @author Emina Torlak
   */
  public interface Indexer<K> {
  
  	
  	/**
  	 * Returns the index of the given key, if it is in this.keys.
  	 * Otherwise returns a negative number.
  	 * @return key in this.keys => this.indices[key], {i: int | i < 0 }
  	 */
  	public abstract int indexOf(K key);
  	
  	/**
  	 * Returns the key at the given index.
  	 * @return this.indices.index
  	 * @throws IndexOutOfBoundsException  index !in this.indices[this.keys]
  	 */
  	public abstract K keyAt(int index);
  	
  	/**
  	 * Returns the number of keys in this.indexer.
  	 * @return #this.keys
  	 */
  	public abstract int size();
  	
  	
  }
  