content: /* Alloy Analyzer 4 -- Copyright (c) 2006-2009, Felix Chang
   *
   * 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 edu.mit.csail.sdg.alloy4;
  
  import java.io.Serializable;
  
  /**
   * Immutable; stores a pair of object references; Pair.equals() compares by
   * calling equals() on both components.
   * <p>
   * <b>Thread Safety:</b> Safe (since objects of this class are immutable).
   */
  
  public final class Pair<A, B> implements Serializable {
  
      /** This ensures the class can be serialized reliably. */
      private static final long serialVersionUID = 0;
  
      /** The first half of the pair. */
      public final A            a;
  
      /** The second half of the pair. */
      public final B            b;
  
      /** Constructs a new Pair object (a,b). */
      public Pair(A a, B b) {
          this.a = a;
          this.b = b;
      }
  
      /**
       * If "a" and "b" are both String, concatename them with a space; if only one
       * is, return it; else call toString() on them.
       */
      @Override
      public String toString() {
          if (a instanceof String) {
              if (b instanceof String)
                  return a + " " + b;
              else
                  return (String) a;
          }
          if (b instanceof String)
              return (String) b;
          if (a == null) {
              return (b != null) ? b.toString() : "";
          } else {
              return (b != null) ? (a + " " + b) : a.toString();
          }
      }
  
      /**
       * Returns a hashcode based on (a==null?0:a.hashCode()) and
       * (b==null?0:b.hashCode()).
       */
      @Override
      public int hashCode() {
          int i = (a == null) ? 0 : a.hashCode();
          int j = (b == null) ? 0 : b.hashCode();
          return i * 173123 + j;
      }
  
      /**
       * Pairs (a1, b1) and (a2, b2) are equal iff (a1==null ? a2==null :
       * a1.equals(a2)) and (b1==null ? b2==null : b1.equals(b2))
       */
      @Override
      public boolean equals(Object that) {
          if (this == that)
              return true;
          if (!(that instanceof Pair))
              return false;
          Pair< ? , ? > p = (Pair< ? , ? >) that;
          return (a == null ? p.a == null : a.equals(p.a)) && (b == null ? p.b == null : b.equals(p.b));
      }
  }
  