class/corlib/System.Collections.Generic/EqualityComparer.cs

   1 //
   2 // Comparer
   3 //
   4 // Authors:
   5 //      Ben Maurer (bmaurer@ximian.com)
   6 //
   7 // Copyright (C) 2004 Novell, Inc (http://www.novell.com)
   8 //
   9 // Permission is hereby granted, free of charge, to any person obtaining
  10 // a copy of this software and associated documentation files (the
  11 // "Software"), to deal in the Software without restriction, including
  12 // without limitation the rights to use, copy, modify, merge, publish,
  13 // distribute, sublicense, and/or sell copies of the Software, and to
  14 // permit persons to whom the Software is furnished to do so, subject to
  15 // the following conditions:
  16 //
  17 // The above copyright notice and this permission notice shall be
  18 // included in all copies or substantial portions of the Software.
  19 //
  20 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  21 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  22 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  23 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  24 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  25 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  26 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  27 //
  28
  29 using System;
  30 using System.Runtime.InteropServices;
  31
  32 namespace System.Collections.Generic {
  33         [Serializable]
  34         public abstract class EqualityComparer <T> : IEqualityComparer, IEqualityComparer <T> {
  35
  36                 static EqualityComparer ()
  37                 {
  38                         if (typeof (IEquatable <T>).IsAssignableFrom (typeof (T)))
  39                                 _default = (EqualityComparer <T>) Activator.CreateInstance (typeof (GenericEqualityComparer <>).MakeGenericType (typeof (T)));
  40                         else
  41                                 _default = new DefaultComparer ();
  42                 }
  43
  44
  45                 public abstract int GetHashCode (T obj);
  46                 public abstract bool Equals (T x, T y);
  47
  48                 static readonly EqualityComparer <T> _default;
  49
  50                 public static EqualityComparer <T> Default {
  51                         get {
  52                                 return _default;
  53                         }
  54                 }
  55
  56                 int IEqualityComparer.GetHashCode (object obj)
  57                 {
  58                         return GetHashCode ((T)obj);
  59                 }
  60
  61                 bool IEqualityComparer.Equals (object x, object y)
  62                 {
  63                         if (!(x is T))
  64                                 throw new ArgumentException ("Argument is not compatible", "x");
  65                         if (!(y is T))
  66                                 throw new ArgumentException ("Argument is not compatible", "y");
  67                         return Equals ((T)x, (T)y);
  68                 }
  69
  70                 [Serializable]
  71                 sealed class DefaultComparer : EqualityComparer<T> {
  72
  73                         public override int GetHashCode (T obj)
  74                         {
  75                                 if (obj == null)
  76                                         return 0;
  77                                 return obj.GetHashCode ();
  78                         }
  79
  80                         public override bool Equals (T x, T y)
  81                         {
  82                                 if (x == null)
  83                                         return y == null;
  84
  85                                 return x.Equals (y);
  86                         }
  87                 }
  88         }
  89
  90         [Serializable]
  91 #if MONOTOUCH
  92         internal
  93 #endif
  94         sealed class GenericEqualityComparer <T> : EqualityComparer <T> where T : IEquatable <T> {
  95
  96                 public override int GetHashCode (T obj)
  97                 {
  98                         if (obj == null)
  99                                 return 0;
 100                         return obj.GetHashCode ();
 101                 }
 102
 103                 public override bool Equals (T x, T y)
 104                 {
 105                         if (x == null)
 106                                 return y == null;
 107
 108                         return x.Equals (y);
 109                 }
 110         }
 111 }