src/System.Private.CoreLib/shared/System/Collections/Generic/NonRandomizedStringEqualityComparer.cs


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// 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.

using System.Runtime.Serialization;

namespace System.Collections.Generic
{
    // NonRandomizedStringEqualityComparer is the comparer used by default with the Dictionary<string,...> 
    // We use NonRandomizedStringEqualityComparer as default comparer as it doesnt use the randomized string hashing which 
    // keeps the performance not affected till we hit collision threshold and then we switch to the comparer which is using 
    // randomized string hashing.
    [Serializable] // Required for compatibility with .NET Core 2.0 as we exposed the NonRandomizedStringEqualityComparer inside the serialization blob
    // Needs to be public to support binary serialization compatibility
    public sealed class NonRandomizedStringEqualityComparer : EqualityComparer<string>, ISerializable
    {
        internal static new IEqualityComparer<string> Default { get; } = new NonRandomizedStringEqualityComparer();

        private NonRandomizedStringEqualityComparer() { }

        // This is used by the serialization engine.
        private NonRandomizedStringEqualityComparer(SerializationInfo information, StreamingContext context) { }

        public sealed override bool Equals(string x, string y) => string.Equals(x, y);

        public sealed override int GetHashCode(string obj) => obj?.GetNonRandomizedHashCode() ?? 0;

        public void GetObjectData(SerializationInfo info, StreamingContext context)
        {
            // We are doing this to stay compatible with .NET Framework.
            info.SetType(typeof(GenericEqualityComparer<string>));
        }
    }
}