mono/mcs/class/corlib/System.Collections.Generic/Comparer.cs

//
// Comparer
//
// Authors:
//	Ben Maurer ([email protected])
//
// Copyright (C) 2004 Novell, Inc (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
// 
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

#if NET_2_0
using System;
using System.Runtime.InteropServices;

namespace System.Collections.Generic {
	[Serializable]
	public abstract class Comparer<T> : IComparer<T>, System.Collections.IComparer {
		
		static Comparer ()
		{
			if (typeof (IComparable<T>).IsAssignableFrom (typeof (T)))
				_default = (Comparer<T>) Activator.CreateInstance (typeof (IComparableOfTComparer <>).MakeGenericType (typeof (T)));
			else
				_default = new DefaultComparer ();
		}
		
		
		public abstract int Compare (T x, T y);
	
		static readonly Comparer <T> _default;
		
		public static Comparer <T> Default {
			get {
				return _default;
			}
		}
	
		int System.Collections.IComparer.Compare (object x, object y)
		{
			
			if (x == null)
				return y == null ? 0 : -1;
			if (y == null)
				return 1;
			
			if (x is T && y is T)
				return Compare ((T) x, (T) y);
			
			throw new ArgumentException ();
		}
	
		class DefaultComparer : Comparer<T> {
	
			public override int Compare (T x, T y)
			{
				// `null' is less than any other ref type
				if (x == null)
					return y == null ? 0 : -1;
				else if (y == null)
					return 1;
	
				if (x is IComparable<T>)
					return ((IComparable<T>) x).CompareTo (y);
				else if (x is IComparable)
					return ((IComparable) x).CompareTo (y);
				else
					throw new ArgumentException ("does not implement right interface");
			}
		}
	}
	
	class IComparableOfTComparer <T> : Comparer <T> where T : IComparable {
		public override int Compare (T x, T y)
		{
			// `null' is less than any other ref type
			if (x == null)
				return y == null ? 0 : -1;
			else if (y == null)
				return 1;
			
			return x.CompareTo (y);
		}
	}

}
#endif