5 // Ben Maurer (bmaurer@ximian.com)
7 // Copyright (C) 2004 Novell, Inc (http://www.novell.com)
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:
17 // The above copyright notice and this permission notice shall be
18 // included in all copies or substantial portions of the Software.
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.
30 using System.Runtime.InteropServices;
32 namespace System.Collections.Generic {
34 public abstract class EqualityComparer <T> : IEqualityComparer, IEqualityComparer <T> {
36 static EqualityComparer ()
38 if (typeof (T) == typeof (string)){
39 _default = (EqualityComparer<T>) (object) new InternalStringComparer ();
42 if (typeof (IEquatable <T>).IsAssignableFrom (typeof (T)))
43 _default = (EqualityComparer <T>) Activator.CreateInstance (typeof (GenericEqualityComparer <>).MakeGenericType (typeof (T)));
45 _default = new DefaultComparer ();
49 public abstract int GetHashCode (T obj);
50 public abstract bool Equals (T x, T y);
52 static readonly EqualityComparer <T> _default;
54 public static EqualityComparer <T> Default {
60 int IEqualityComparer.GetHashCode (object obj)
62 return GetHashCode ((T)obj);
65 bool IEqualityComparer.Equals (object x, object y)
68 throw new ArgumentException ("Argument is not compatible", "x");
70 throw new ArgumentException ("Argument is not compatible", "y");
71 return Equals ((T)x, (T)y);
75 sealed class DefaultComparer : EqualityComparer<T> {
77 public override int GetHashCode (T obj)
81 return obj.GetHashCode ();
84 public override bool Equals (T x, T y)
95 sealed class InternalStringComparer : EqualityComparer<string> {
97 public override int GetHashCode (string obj)
101 return obj.GetHashCode ();
104 public override bool Equals (string x, string y)
109 if ((object) x == (object) y)
117 sealed class GenericEqualityComparer <T> : EqualityComparer <T> where T : IEquatable <T> {
119 public override int GetHashCode (T obj)
123 return obj.GetHashCode ();
126 public override bool Equals (T x, T y)