StringComparer.cs

// Copyright (c) Microsoft. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.


namespace System {
    using System.Collections;
    using System.Collections.Generic;    
    using System.Globalization;
    using System.Diagnostics.Contracts;
    using System.Runtime.Serialization;
    using System.Runtime.CompilerServices;


    [Serializable]
    [System.Runtime.InteropServices.ComVisible(true)]
    public abstract class StringComparer : IComparer, IEqualityComparer, IComparer<string>, IEqualityComparer<string>{
        private static readonly StringComparer _invariantCulture = new CultureAwareComparer(CultureInfo.InvariantCulture, false);        
        private static readonly StringComparer _invariantCultureIgnoreCase = new CultureAwareComparer(CultureInfo.InvariantCulture, true);      
        private static readonly StringComparer _ordinal = new OrdinalComparer(false);
        private static readonly StringComparer _ordinalIgnoreCase = new OrdinalComparer(true);        

        public static StringComparer InvariantCulture { 
            get {
                Contract.Ensures(Contract.Result<StringComparer>() != null);
                return _invariantCulture;
            }
        }
        
        public static StringComparer InvariantCultureIgnoreCase { 
            get {
                Contract.Ensures(Contract.Result<StringComparer>() != null);
                return _invariantCultureIgnoreCase;
            }
        }

        public static StringComparer CurrentCulture { 
            get {
                Contract.Ensures(Contract.Result<StringComparer>() != null);
                return new CultureAwareComparer(CultureInfo.CurrentCulture, false);                
            }
        }
        
        public static StringComparer CurrentCultureIgnoreCase { 
            get {
                Contract.Ensures(Contract.Result<StringComparer>() != null);
                return new CultureAwareComparer(CultureInfo.CurrentCulture, true);                
            }
        }

        public static StringComparer Ordinal { 
            get {
                Contract.Ensures(Contract.Result<StringComparer>() != null);
                return _ordinal;
            }
        }

        public static StringComparer OrdinalIgnoreCase { 
            get {
                Contract.Ensures(Contract.Result<StringComparer>() != null);
                return _ordinalIgnoreCase;
            }
        }

        public static StringComparer Create(CultureInfo culture, bool ignoreCase) {
            if( culture == null) {
                throw new ArgumentNullException("culture");
            }
            Contract.Ensures(Contract.Result<StringComparer>() != null);
            Contract.EndContractBlock();
            
            return new CultureAwareComparer(culture, ignoreCase);            
        }  

        public int Compare(object x, object y) {
            if (x == y) return 0;
            if (x == null) return -1;
            if (y == null) return 1;
                        
            String sa = x as String;
            if (sa != null) {                
                String sb = y as String;                
                if( sb != null) {
                    return Compare(sa, sb);                    
                }
            }

            IComparable ia = x as IComparable;
            if (ia != null) {
                return ia.CompareTo(y);
            }

            throw new ArgumentException(Environment.GetResourceString("Argument_ImplementIComparable"));            
        }

       
        public new bool Equals(Object x, Object y) {
            if (x == y) return true;
            if (x == null || y == null) return false;
            
            String sa = x as String;
            if (sa != null) {
                String sb = y as String;                
                if( sb != null) {
                    return Equals(sa, sb);
                }
            }
            return x.Equals(y);                        
        }
        
        public int GetHashCode(object obj) {
            if( obj == null) {
                throw new ArgumentNullException("obj");
            }
            Contract.EndContractBlock();

            string s = obj as string;
            if( s != null) {
                return GetHashCode(s);
            }
            return obj.GetHashCode();            
        }
        
        public abstract int Compare(String x, String y);
        public abstract bool Equals(String x, String y);        
        public abstract int GetHashCode(string obj);        
    }
    
    [Serializable]
    internal sealed class CultureAwareComparer : StringComparer
#if FEATURE_RANDOMIZED_STRING_HASHING
        , IWellKnownStringEqualityComparer 
#endif
    {
        private CompareInfo _compareInfo;    
        private bool            _ignoreCase;

        internal CultureAwareComparer(CultureInfo culture, bool ignoreCase) {
               _compareInfo = culture.CompareInfo;
               _ignoreCase = ignoreCase;
        }

        internal CultureAwareComparer(CompareInfo compareInfo, bool ignoreCase) {
               _compareInfo = compareInfo;
               _ignoreCase = ignoreCase;
        }

        public override int Compare(string x, string y) {
            if (Object.ReferenceEquals(x, y)) return 0;
            if (x == null) return -1;
            if (y == null) return 1;
            return _compareInfo.Compare(x, y, _ignoreCase? CompareOptions.IgnoreCase :  CompareOptions.None);
        }
                
        public override bool Equals(string x, string y) {
            if (Object.ReferenceEquals(x ,y)) return true;
            if (x == null || y == null) return false;

            return (_compareInfo.Compare(x, y, _ignoreCase? CompareOptions.IgnoreCase :  CompareOptions.None) == 0);
        }               
                
        public override int GetHashCode(string obj) {
            if( obj == null) {
                throw new ArgumentNullException("obj");
            }
            Contract.EndContractBlock();

            CompareOptions options = CompareOptions.None;

            if( _ignoreCase) {
                options |= CompareOptions.IgnoreCase;
            }

            return _compareInfo.GetHashCodeOfString(obj, options);
        }       

        // Equals method for the comparer itself. 
        public override bool Equals(Object obj){
            CultureAwareComparer comparer = obj as CultureAwareComparer;
            if( comparer == null) {
                return false;
            }
            return (this._ignoreCase == comparer._ignoreCase) && (this._compareInfo.Equals(comparer._compareInfo));
        }

        public override int GetHashCode() {
            int hashCode = _compareInfo.GetHashCode() ;
            return _ignoreCase ? (~hashCode) : hashCode;
        }

#if FEATURE_RANDOMIZED_STRING_HASHING           
        IEqualityComparer IWellKnownStringEqualityComparer.GetRandomizedEqualityComparer() {
            return new CultureAwareRandomizedComparer(_compareInfo, _ignoreCase);
        }

        IEqualityComparer IWellKnownStringEqualityComparer.GetEqualityComparerForSerialization() {
            return this;
        }
#endif

    }

#if FEATURE_RANDOMIZED_STRING_HASHING
    internal sealed class CultureAwareRandomizedComparer : StringComparer, IWellKnownStringEqualityComparer {

        private CompareInfo _compareInfo;    
        private bool        _ignoreCase;
        private long        _entropy;

        internal CultureAwareRandomizedComparer(CompareInfo compareInfo, bool ignoreCase) {
               _compareInfo = compareInfo;
               _ignoreCase = ignoreCase;
               _entropy = HashHelpers.GetEntropy();
        }

        public override int Compare(string x, string y) {
            if (Object.ReferenceEquals(x, y)) return 0;
            if (x == null) return -1;
            if (y == null) return 1;
            return _compareInfo.Compare(x, y, _ignoreCase? CompareOptions.IgnoreCase :  CompareOptions.None);
        }
                
        public override bool Equals(string x, string y) {
            if (Object.ReferenceEquals(x ,y)) return true;
            if (x == null || y == null) return false;

            return (_compareInfo.Compare(x, y, _ignoreCase? CompareOptions.IgnoreCase :  CompareOptions.None) == 0);
        }               
                
        public override int GetHashCode(string obj) {
            if( obj == null) {
                throw new ArgumentNullException("obj");
            }
            Contract.EndContractBlock();

            CompareOptions options = CompareOptions.None;

            if( _ignoreCase) {
                options |= CompareOptions.IgnoreCase;
            }

#if FEATURE_COREFX_GLOBALIZATION
            return _compareInfo.GetHashCodeOfStringCore(obj, options, true, _entropy);
#else
            return _compareInfo.GetHashCodeOfString(obj, options, true, _entropy);
#endif
        }       

        // Equals method for the comparer itself. 
        public override bool Equals(Object obj){
            CultureAwareRandomizedComparer comparer = obj as CultureAwareRandomizedComparer;
            if( comparer == null) {
                return false;
            }
            return (this._ignoreCase == comparer._ignoreCase) && (this._compareInfo.Equals(comparer._compareInfo)) && (this._entropy == comparer._entropy);
        }

        public override int GetHashCode() {
            int hashCode = _compareInfo.GetHashCode() ;
            return ((_ignoreCase ? (~hashCode) : hashCode) ^ ((int) (_entropy & 0x7FFFFFFF)));
        }

        IEqualityComparer IWellKnownStringEqualityComparer.GetRandomizedEqualityComparer() {
            return new CultureAwareRandomizedComparer(_compareInfo, _ignoreCase);
        }

        // We want to serialize the old comparer.
        IEqualityComparer IWellKnownStringEqualityComparer.GetEqualityComparerForSerialization() {
            return new CultureAwareComparer(_compareInfo, _ignoreCase);
        }
    }
#endif

    // Provide x more optimal implementation of ordinal comparison.
    [Serializable]
    internal sealed class OrdinalComparer : StringComparer 
#if FEATURE_RANDOMIZED_STRING_HASHING           
        , IWellKnownStringEqualityComparer
#endif
    {
        private bool            _ignoreCase;
       
        internal OrdinalComparer(bool ignoreCase) {
               _ignoreCase = ignoreCase;
        }

        public override int Compare(string x, string y) {
            if (Object.ReferenceEquals(x, y)) return 0;
            if (x == null) return -1;
            if (y == null) return 1;
            
            if( _ignoreCase) {
                return String.Compare(x, y, StringComparison.OrdinalIgnoreCase);
            }
                    
            return String.CompareOrdinal(x, y);                                
        }
                
        public override bool Equals(string x, string y) {
            if (Object.ReferenceEquals(x ,y)) return true;
            if (x == null || y == null) return false;

            if( _ignoreCase) {
                if( x.Length != y.Length) {
                    return false;
                }
                return (String.Compare(x, y, StringComparison.OrdinalIgnoreCase) == 0);                                            
            }
            return x.Equals(y);
        }               
                
        public override int GetHashCode(string obj) {
            if( obj == null) {
                throw new ArgumentNullException("obj");
            }
            Contract.EndContractBlock();

            if( _ignoreCase) {
                return TextInfo.GetHashCodeOrdinalIgnoreCase(obj);
            }
                        
            return obj.GetHashCode();
        }       

        // Equals method for the comparer itself. 
        public override bool Equals(Object obj){
            OrdinalComparer comparer = obj as OrdinalComparer;
            if( comparer == null) {
                return false;
            }
            return (this._ignoreCase == comparer._ignoreCase);
        }

        public override int GetHashCode() {
            string name = "OrdinalComparer";
            int hashCode = name.GetHashCode();
            return _ignoreCase ? (~hashCode) : hashCode;
        }

#if FEATURE_RANDOMIZED_STRING_HASHING           
        IEqualityComparer IWellKnownStringEqualityComparer.GetRandomizedEqualityComparer() {
            return new OrdinalRandomizedComparer(_ignoreCase);
        }

        IEqualityComparer IWellKnownStringEqualityComparer.GetEqualityComparerForSerialization() {
            return this;
        }
#endif
                                
    }


#if FEATURE_RANDOMIZED_STRING_HASHING           
    internal sealed class OrdinalRandomizedComparer : StringComparer, IWellKnownStringEqualityComparer {
        private bool            _ignoreCase;
        private long            _entropy;
       
        internal OrdinalRandomizedComparer(bool ignoreCase) {
               _ignoreCase = ignoreCase;
               _entropy = HashHelpers.GetEntropy();
        }

        public override int Compare(string x, string y) {
            if (Object.ReferenceEquals(x, y)) return 0;
            if (x == null) return -1;
            if (y == null) return 1;
            
            if( _ignoreCase) {
                return String.Compare(x, y, StringComparison.OrdinalIgnoreCase);
            }
                    
            return String.CompareOrdinal(x, y);                                
        }
                
        public override bool Equals(string x, string y) {
            if (Object.ReferenceEquals(x ,y)) return true;
            if (x == null || y == null) return false;

            if( _ignoreCase) {
                if( x.Length != y.Length) {
                    return false;
                }
                return (String.Compare(x, y, StringComparison.OrdinalIgnoreCase) == 0);                                            
            }
            return x.Equals(y);
        }               

        [System.Security.SecuritySafeCritical]            
        public override int GetHashCode(string obj) {
            if( obj == null) {
                throw new ArgumentNullException("obj");
            }
            Contract.EndContractBlock();

            if( _ignoreCase) {
#if FEATURE_COREFX_GLOBALIZATION
                return CultureInfo.InvariantCulture.CompareInfo.GetHashCodeOfStringCore(obj, CompareOptions.IgnoreCase, true, _entropy);
#else
                return TextInfo.GetHashCodeOrdinalIgnoreCase(obj, true, _entropy);
#endif
            }
                        
            return String.InternalMarvin32HashString(obj, obj.Length, _entropy);
        }       

        // Equals method for the comparer itself. 
        public override bool Equals(Object obj){
            OrdinalRandomizedComparer comparer = obj as OrdinalRandomizedComparer;
            if( comparer == null) {
                return false;
            }
            return (this._ignoreCase == comparer._ignoreCase) && (this._entropy == comparer._entropy);
        }

        public override int GetHashCode() {
            string name = "OrdinalRandomizedComparer";
            int hashCode = name.GetHashCode();
            return ((_ignoreCase ? (~hashCode) : hashCode) ^ ((int) (_entropy & 0x7FFFFFFF)));
        }

        IEqualityComparer IWellKnownStringEqualityComparer.GetRandomizedEqualityComparer() {
            return new OrdinalRandomizedComparer(_ignoreCase);
        }

        // We want to serialize the old comparer.
        IEqualityComparer IWellKnownStringEqualityComparer.GetEqualityComparerForSerialization() {
            return new OrdinalComparer(_ignoreCase);
        }                                
    }

    // This interface is implemented by string comparers in the framework that can opt into
    // randomized hashing behaviors. 
    internal interface IWellKnownStringEqualityComparer {
        // Get an IEqualityComparer that has the same equality comparision rules as "this" but uses Randomized Hashing.
        IEqualityComparer GetRandomizedEqualityComparer();
        // Get an IEqaulityComparer that can be serailzied (e.g., it exists in older versions). 
        IEqualityComparer GetEqualityComparerForSerialization();
    }
#endif
}