class/corlib/System.Collections.Generic/Comparer.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 Comparer<T> : IComparer<T>, System.Collections.IComparer {
  35
  36                 static Comparer ()
  37                 {
  38                         if (typeof (IComparable<T>).IsAssignableFrom (typeof (T)))
  39                                 _default = (Comparer<T>) Activator.CreateInstance (typeof (GenericComparer <>).MakeGenericType (typeof (T)));
  40                         else
  41                                 _default = new DefaultComparer ();
  42                 }
  43
  44                 public abstract int Compare (T x, T y);
  45
  46                 static readonly Comparer <T> _default;
  47
  48                 public static Comparer <T> Default {
  49                         get {
  50                                 return _default;
  51                         }
  52                 }
  53
  54                 int System.Collections.IComparer.Compare (object x, object y)
  55                 {
  56
  57                         if (x == null)
  58                                 return y == null ? 0 : -1;
  59                         if (y == null)
  60                                 return 1;
  61
  62                         if (x is T && y is T)
  63                                 return Compare ((T) x, (T) y);
  64
  65                         throw new ArgumentException ();
  66                 }
  67
  68                 sealed class DefaultComparer : Comparer<T> {
  69
  70                         public override int Compare (T x, T y)
  71                         {
  72                                 // `null' is less than any other ref type
  73                                 if (x == null)
  74                                         return y == null ? 0 : -1;
  75                                 else if (y == null)
  76                                         return 1;
  77
  78                                 if (x is IComparable<T>)
  79                                         return ((IComparable<T>) x).CompareTo (y);
  80                                 else if (x is IComparable)
  81                                         return ((IComparable) x).CompareTo (y);
  82                                 else
  83                                         throw new ArgumentException ("does not implement right interface");
  84                         }
  85                 }
  86         }
  87
  88         [Serializable]
  89         sealed class GenericComparer <T> : Comparer <T> where T : IComparable<T> {
  90                 public override int Compare (T x, T y)
  91                 {
  92                         // `null' is less than any other ref type
  93                         if (x == null)
  94                                 return y == null ? 0 : -1;
  95                         else if (y == null)
  96                                 return 1;
  97
  98                         return x.CompareTo (y);
  99                 }
 100         }
 101
 102 }