Илья

var d = new Dictionary<string, string>();
d.Add("a", "a");
Console.WriteLine(d.ElementAt(0).Value);

using System;
using System.Text;

namespace Sample
{
    internal static class StringExtentions
    {
        public static string CustomReplace(this string origin, string from, string to, StringComparison stringComparison = StringComparison.Ordinal)
        {
            var sb = new StringBuilder();
            
            int position = 0;
            do
            {
                var quoteStart = origin.IndexOf('"', position);
                if (quoteStart == -1)
                    quoteStart = origin.Length;
                var headLength = quoteStart - position;
                if (headLength > 0)
                {
                    sb.Append(origin.Substring(position, headLength).Replace(from, to, stringComparison));
                }

                position = quoteStart;
                if(position == origin.Length) break;
                
                var quoteEnd = origin.IndexOf('"', position + 1);
                if (quoteEnd == -1)
                    quoteEnd = origin.Length;

                var tailLength = quoteEnd + 1 - position;
                if (tailLength > 0)
                {
                    sb.Append(origin.Substring(position, tailLength));
                }
                
                position = quoteEnd + 1;

            } while (position < origin.Length);
            
            return sb.ToString();
        }
    }
    
    internal class Program
    {
        private static void Main(string[] args)
        {
            Console.WriteLine("Я сказал: \"БАНАН не банан\", но банан не согласен со мной. Но я отвечу этому банану: \"бананством\"".CustomReplace("банан", "яблоко", StringComparison.OrdinalIgnoreCase));
        }
    }
}

int[] array = {1, 1, 1, 2, 3, 3, 4, 4, 4, 4, 5, 6, 6, 7, 8};
var sortedByFrequency = array
    .GroupBy(o => o)
    .OrderByDescending(o => o.Count())
    .ThenByDescending(o => o.Key)
    .SelectMany(o => o)
    .ToArray();
Console.WriteLine(string.Join(",",sortedByFrequency.Select(o => o.ToString())));
//4,4,4,4,1,1,1,6,6,3,3,8,7,5,2

foreach (var descriptor in serviceCollection)
{
     services.Add(descriptor);
}

internal class PackageInfo : PackageInfo<FrameType, Frame>
{
    public PackageInfo(FrameType key, Frame body) : base(key, body)
    {
    }
}

internal class ReceiveFilter : FixedHeaderReceiveFilter<PackageInfo>
{
    public ReceiveFilter(int headerSize) : base(headerSize)
    {
    }

    public override PackageInfo ResolvePackage(IBufferStream bufferStream)
    {
        //реализация получения пакета из потока
    }
    

    protected override int GetBodyLengthFromHeader(IBufferStream bufferStream, int length)
    {
        var frameLength = bufferStream.ReadInt32(true);
        return frameLength - HeaderSize;
    }
}

var client = new EasyClient<PackageInfo>();
client.Initialize(new ReceiveFilter(4));
client.NoDelay = true;
client.ReceiveBufferSize = 10240;
client.NewPackageReceived += NewPackageReceived;