mono/netcore/System.Private.CoreLib/shared/System/Collections/Comparer.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

/*============================================================
**
** Purpose: Default IComparer implementation.
**
===========================================================*/

using System.Globalization;
using System.Runtime.Serialization;

namespace System.Collections
{
    [Serializable]
    [System.Runtime.CompilerServices.TypeForwardedFrom("mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089")]
    public sealed class Comparer : IComparer, ISerializable
    {
        private CompareInfo _compareInfo;

        public static readonly Comparer Default = new Comparer(CultureInfo.CurrentCulture);
        public static readonly Comparer DefaultInvariant = new Comparer(CultureInfo.InvariantCulture);

        public Comparer(CultureInfo culture)
        {
            if (culture == null)
                throw new ArgumentNullException(nameof(culture));

            _compareInfo = culture.CompareInfo;
        }

        private Comparer(SerializationInfo info, StreamingContext context)
        {
            if (info == null)
                throw new ArgumentNullException(nameof(info));

            _compareInfo = (CompareInfo)info.GetValue("CompareInfo", typeof(CompareInfo));
        }

        public void GetObjectData(SerializationInfo info, StreamingContext context)
        {
            if (info == null)
                throw new ArgumentNullException(nameof(info));

            info.AddValue("CompareInfo", _compareInfo);
        }

        // Compares two Objects by calling CompareTo.
        // If a == b, 0 is returned.
        // If a implements IComparable, a.CompareTo(b) is returned.
        // If a doesn't implement IComparable and b does, -(b.CompareTo(a)) is returned.
        // Otherwise an exception is thrown.
        // 
        public int Compare(object a, object b)
        {
            if (a == b) return 0;
            if (a == null) return -1;
            if (b == null) return 1;

            string sa = a as string;
            string sb = b as string;
            if (sa != null && sb != null)
                return _compareInfo.Compare(sa, sb);

            IComparable ia = a as IComparable;
            if (ia != null)
                return ia.CompareTo(b);

            IComparable ib = b as IComparable;
            if (ib != null)
                return -ib.CompareTo(a);

            throw new ArgumentException(SR.Argument_ImplementIComparable);
        }
    }
}