Comparer.cs source code in C# .NET

                        
Code:
                         / DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / clr / src / BCL / System / Collections / Generic / Comparer.cs / 1 / Comparer.cs
                        

                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 

using System; 
using System.Collections; 
using System.Collections.Generic;
 
namespace System.Collections.Generic
{
    using System.Globalization;
    using System.Runtime.CompilerServices; 

    [Serializable()] 
    [TypeDependencyAttribute("System.Collections.Generic.GenericComparer`1")] 
    public abstract class Comparer : IComparer, IComparer
    { 
        static Comparer defaultComparer;

        public static Comparer Default {
            get { 
                Comparer comparer = defaultComparer;
                if (comparer == null) { 
                    comparer = CreateComparer(); 
                    defaultComparer = comparer;
                } 
                return comparer;
            }
        }
 
        private static Comparer CreateComparer() {
            Type t = typeof(T); 
            // If T implements IComparable return a GenericComparer 
            if (typeof(IComparable).IsAssignableFrom(t)) {
                //return (Comparer)Activator.CreateInstance(typeof(GenericComparer<>).MakeGenericType(t)); 
                return (Comparer)(typeof(GenericComparer).TypeHandle.CreateInstanceForAnotherGenericParameter(t));
            }
            // If T is a Nullable where U implements IComparable return a NullableComparer
            if (t.IsGenericType && t.GetGenericTypeDefinition() == typeof(Nullable<>)) { 
                Type u = t.GetGenericArguments()[0];
                if (typeof(IComparable<>).MakeGenericType(u).IsAssignableFrom(u)) { 
                    //return (Comparer)Activator.CreateInstance(typeof(NullableComparer<>).MakeGenericType(u)); 
                    return (Comparer)(typeof(NullableComparer).TypeHandle.CreateInstanceForAnotherGenericParameter(u));
                } 
            }
            // Otherwise return an ObjectComparer
            return new ObjectComparer();
        } 

        public abstract int Compare(T x, T y); 
 
        int 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);
            ThrowHelper.ThrowArgumentException(ExceptionResource.Argument_InvalidArgumentForComparison);
            return 0; 
        }
    } 
 
    [Serializable()]
    internal class GenericComparer : Comparer where T: IComparable 
    {
        public override int Compare(T x, T y) {
            if (x != null) {
                if (y != null) return x.CompareTo(y); 
                return 1;
            } 
            if (y != null) return -1; 
            return 0;
        } 

        // Equals method for the comparer itself.
        public override bool Equals(Object obj){
            GenericComparer comparer = obj as GenericComparer; 
            return comparer != null;
        } 
 
        public override int GetHashCode() {
            return this.GetType().Name.GetHashCode(); 
        }
    }

    [Serializable()] 
    internal class NullableComparer : Comparer> where T : struct, IComparable
    { 
        public override int Compare(Nullable x, Nullable y) { 
            if (x.HasValue) {
                if (y.HasValue) return x.value.CompareTo(y.value); 
                return 1;
            }
            if (y.HasValue) return -1;
            return 0; 
        }
 
        // Equals method for the comparer itself. 
        public override bool Equals(Object obj){
            NullableComparer comparer = obj as NullableComparer; 
            return comparer != null;
        }

        public override int GetHashCode() { 
            return this.GetType().Name.GetHashCode();
        } 
    } 

    [Serializable()] 
    internal class ObjectComparer : Comparer
    {
        public override int Compare(T x, T y) {
            return System.Collections.Comparer.Default.Compare(x, y); 
        }
 
        // Equals method for the comparer itself. 
        public override bool Equals(Object obj){
            ObjectComparer comparer = obj as ObjectComparer; 
            return comparer != null;
        }

        public override int GetHashCode() { 
            return this.GetType().Name.GetHashCode();
        } 
    } 
}