mcs/class/referencesource/mscorlib/system/collections/comparer.cs

   1 // ==++==
   2 //
   3 //   Copyright (c) Microsoft Corporation.  All rights reserved.
   4 //
   5 // ==--==
   6 /*============================================================
   7 **
   8 ** Class:  Comparer
   9 **
  10 ** <OWNER>Microsoft</OWNER>
  11 **
  12 **
  13 ** Purpose: Default IComparer implementation.
  14 **
  15 **
  16 ===========================================================*/
  17 namespace System.Collections {
  18
  19     using System;
  20     using System.Globalization;
  21     using System.Runtime.Serialization;
  22     using System.Security.Permissions;
  23     using System.Diagnostics.Contracts;
  24
  25     [Serializable]
  26 [System.Runtime.InteropServices.ComVisible(true)]
  27     public sealed class Comparer : IComparer , ISerializable
  28     {
  29         private CompareInfo m_compareInfo;
  30         public static readonly Comparer Default = new Comparer(CultureInfo.CurrentCulture);
  31         public static readonly Comparer DefaultInvariant = new Comparer(CultureInfo.InvariantCulture);
  32
  33         private const String CompareInfoName = "CompareInfo";
  34
  35         private Comparer() {
  36             m_compareInfo = null;
  37         }
  38
  39         public Comparer(CultureInfo culture) {
  40             if (culture==null) {
  41                 throw new ArgumentNullException("culture");
  42             }
  43             Contract.EndContractBlock();
  44             m_compareInfo = culture.CompareInfo;
  45         }
  46
  47         private Comparer(SerializationInfo info, StreamingContext context) {
  48             m_compareInfo = null;
  49             SerializationInfoEnumerator enumerator = info.GetEnumerator();
  50             while( enumerator.MoveNext()) {
  51                 switch( enumerator.Name) {
  52                     case CompareInfoName:
  53                         m_compareInfo = (CompareInfo) info.GetValue(CompareInfoName, typeof(CompareInfo));
  54                         break;
  55                 }
  56             }
  57         }
  58
  59         // Compares two Objects by calling CompareTo.  If a ==
  60         // b,0 is returned.  If a implements
  61         // IComparable, a.CompareTo(b) is returned.  If a
  62         // doesn't implement IComparable and b does,
  63         // -(b.CompareTo(a)) is returned, otherwise an
  64         // exception is thrown.
  65         //
  66         public int Compare(Object a, Object b) {
  67             if (a == b) return 0;
  68             if (a == null) return -1;
  69             if (b == null) return 1;
  70             if (m_compareInfo != null) {
  71                 String sa = a as String;
  72                 String sb = b as String;
  73                 if (sa != null && sb != null)
  74                     return m_compareInfo.Compare(sa, sb);
  75             }
  76
  77             IComparable ia = a as IComparable;
  78             if (ia != null)
  79                 return ia.CompareTo(b);
  80
  81             IComparable ib = b as IComparable;
  82             if (ib != null)
  83                 return -ib.CompareTo(a);
  84
  85             throw new ArgumentException(Environment.GetResourceString("Argument_ImplementIComparable"));
  86         }
  87
  88         [System.Security.SecurityCritical]  // auto-generated_required
  89         public void GetObjectData(SerializationInfo info, StreamingContext context) {
  90             if (info==null) {
  91                 throw new ArgumentNullException("info");
  92             }
  93             Contract.EndContractBlock();
  94
  95             if( m_compareInfo != null) {
  96                 info.AddValue(CompareInfoName, m_compareInfo);
  97             }
  98         }
  99     }
 100 }