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.
31 using System.Runtime.InteropServices;
33 namespace System.Collections.Generic {
35 public abstract class Comparer<T> : IComparer<T>, System.Collections.IComparer {
39 if (typeof (IComparable<T>).IsAssignableFrom (typeof (T)))
40 _default = (Comparer<T>) Activator.CreateInstance (typeof (IComparableOfTComparer <>).MakeGenericType (typeof (T)));
42 _default = new DefaultComparer ();
46 public abstract int Compare (T x, T y);
48 static readonly Comparer <T> _default;
50 public static Comparer <T> Default {
56 int System.Collections.IComparer.Compare (object x, object y)
60 return y == null ? 0 : -1;
65 return Compare ((T) x, (T) y);
67 throw new ArgumentException ();
70 class DefaultComparer : Comparer<T> {
72 public override int Compare (T x, T y)
74 // `null' is less than any other ref type
76 return y == null ? 0 : -1;
80 if (x is IComparable<T>)
81 return ((IComparable<T>) x).CompareTo (y);
82 else if (x is IComparable)
83 return ((IComparable) x).CompareTo (y);
85 throw new ArgumentException ("does not implement right interface");
90 class IComparableOfTComparer <T> : Comparer <T> where T : IComparable<T> {
91 public override int Compare (T x, T y)
93 // `null' is less than any other ref type
95 return y == null ? 0 : -1;
99 return x.CompareTo (y);