Comparer.cs source code in C# .NET

                        
Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / clr / src / BCL / System / Collections / Generic / Comparer.cs / 1305376 / Comparer.cs
                        

                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
// [....]
// 
 
using System;
using System.Collections; 
using System.Collections.Generic;
using System.Diagnostics.Contracts;
//using System.Globalization;
using System.Runtime.CompilerServices; 

namespace System.Collections.Generic 
{ 
    [Serializable]
    [TypeDependencyAttribute("System.Collections.Generic.GenericComparer`1")] 
    public abstract class Comparer : IComparer, IComparer
    {
        static Comparer defaultComparer;
 
        public static Comparer Default {
            [System.Security.SecuritySafeCritical]  // auto-generated 
            get { 
                Contract.Ensures(Contract.Result>() != null);
 
                Comparer comparer = defaultComparer;
                if (comparer == null) {
                    comparer = CreateComparer();
                    defaultComparer = comparer; 
                }
                return comparer; 
            } 
        }
 
        [System.Security.SecuritySafeCritical]  // auto-generated
        private static Comparer CreateComparer() {
            RuntimeType t = (RuntimeType)typeof(T);
            // If T implements IComparable return a GenericComparer 
            if (typeof(IComparable).IsAssignableFrom(t)) {
                //return (Comparer)Activator.CreateInstance(typeof(GenericComparer<>).MakeGenericType(t)); 
                return (Comparer)RuntimeTypeHandle.CreateInstanceForAnotherGenericParameter((RuntimeType)typeof(GenericComparer), t); 
            }
            // If T is a Nullable where U implements IComparable return a NullableComparer 
            if (t.IsGenericType && t.GetGenericTypeDefinition() == typeof(Nullable<>)) {
                RuntimeType u = (RuntimeType)t.GetGenericArguments()[0];
                if (typeof(IComparable<>).MakeGenericType(u).IsAssignableFrom(u)) {
                    //return (Comparer)Activator.CreateInstance(typeof(NullableComparer<>).MakeGenericType(u)); 
                    return (Comparer)RuntimeTypeHandle.CreateInstanceForAnotherGenericParameter((RuntimeType)typeof(NullableComparer), 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();
        }
    } 
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.