Before we dive into the technical details, let’s start with a quick history lesson, courtesy of Don Syme who worked on adding generics to .NET and then went on to design and implement F#, which is a pretty impressive set of achievements!!

Background and History

• 1999 Initial research, design and planning
  • .NET/C# Generics History: Some Photos From Feb 1999
• 1999 First ‘white paper’ published
  • More C#/.NET Generics Research Project History – The MSR white paper
  • MSR White Paper: Proposed Extensions to COM+ VOS (Draft) (pdf)
• 2001 C# Language Design Specification created
  • Some History: 2001 “GC#” (Generic C#) research project draft
  • MSR - .NET Generics Research Project - Generic C# Specification (pdf)
• 2001 Research paper published
  • Design and Implementation of Generics for the .NET CLR (pdf)
• 2004 Work completed and all bugs fixed
  • Some more .NET/C# Generics Research Project History 

modelBuilder.UseCollation("SQL_Latin1_General_CP1_CS_AS");

public static void SetCaseInsensitiveSearchesForSQLite(this ModelBuilder modelBuilder)
{
    if (modelBuilder == null)
    {
        throw new ArgumentNullException(nameof(modelBuilder));
    }

    modelBuilder.UseCollation("NOCASE");
    foreach (var property in modelBuilder.Model.GetEntityTypes()
                                            .SelectMany(t => t.GetProperties())
                                            .Where(p => p.ClrType == typeof(string)))
    {
        property.SetCollation("NOCASE");
    }
}

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    if (modelBuilder == null)
    {
        throw new ArgumentNullException(nameof(modelBuilder));
    }

    modelBuilder.SetCaseInsensitiveSearchesForSQLite();
}

 <link rel="pingback" href="pingback server">

        private Uri findPingbackServiceUri()
        {
            var request = (HttpWebRequest)WebRequest.Create(_targetUri);
            request.UserAgent = UserAgent;
            request.Timeout = Timeout;
            request.ReadWriteTimeout = Timeout;
            request.Method = WebRequestMethods.Http.Get;
            request.AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate;
            using (var response = request.GetResponse() as HttpWebResponse)
            {
                if (response == null) return null;

                var url = extractPingbackServiceUriFormHeaders(response);
                if (url != null)
                    return url;

                if (!isResponseHtml(response))
                    return null;

                using (var reader = new StreamReader(response.GetResponseStream()))
                {
                    return extractPingbackServiceUriFormPage(reader.ReadToEnd());
                }
            }
        }

        private static Uri extractPingbackServiceUriFormHeaders(WebResponse response)
        {
            var pingUrl = response.Headers.AllKeys.FirstOrDefault(header =>
                                header.Equals("x-pingback", StringComparison.OrdinalIgnoreCase) ||
                                header.Equals("pingback", StringComparison.OrdinalIgnoreCase));

            return getValidAbsoluteUri(pingUrl);
        }

        private static Uri extractPingbackServiceUriFormPage(string content)
        {
            if (string.IsNullOrWhiteSpace(content)) return null;
            var regex = new Regex(@"(?s)<link\srel=""pingback""\shref=""(.+?)""", RegexOptions.IgnoreCase);
            var match = regex.Match(content);
            return (!match.Success || match.Groups.Count < 2) ? null : getValidAbsoluteUri(match.Groups[1].Value);
        }

        private static Uri getValidAbsoluteUri(string url)
        {
            Uri absoluteUri;
            return string.IsNullOrWhiteSpace(url) || !Uri.TryCreate(url, UriKind.Absolute, out absoluteUri) ? null : absoluteUri;
        }

        private static bool isResponseHtml(WebResponse response)
        {
            var contentTypeKey = response.Headers.AllKeys.FirstOrDefault(header =>
                                        header.Equals("content-type", StringComparison.OrdinalIgnoreCase));
            return !string.IsNullOrWhiteSpace(contentTypeKey) &&
                    response.Headers[contentTypeKey].StartsWith("text/html", StringComparison.OrdinalIgnoreCase);
        }

        public void Send()
        {
            var pingUrl = findPingbackServiceUri();
            if (pingUrl == null)
                throw new NotSupportedException(string.Format("{0} doesn't support pingback.", _targetUri.Host));

            sendPing(pingUrl);
        }

        private void sendPing(Uri pingUrl)
        {
            var request = (HttpWebRequest)WebRequest.Create(pingUrl);
            request.UserAgent = UserAgent;
            request.Timeout = Timeout;
            request.ReadWriteTimeout = Timeout;
            request.Method = WebRequestMethods.Http.Post;
            request.ContentType = "text/xml";
            request.ProtocolVersion = HttpVersion.Version11;
            makeXmlRpcRequest(request);
            using (var response = (HttpWebResponse)request.GetResponse())
            {
                response.Close();
            }
        }

        private void makeXmlRpcRequest(WebRequest request)
        {
            var stream = request.GetRequestStream();
            using (var writer = new XmlTextWriter(stream, Encoding.ASCII))
            {
                writer.WriteStartDocument(true);
                writer.WriteStartElement("methodCall");
                writer.WriteElementString("methodName", "pingback.ping");
                writer.WriteStartElement("params");

                writer.WriteStartElement("param");
                writer.WriteStartElement("value");
                writer.WriteElementString("string", Uri.EscapeUriString(_sourceUri.ToString()));
                writer.WriteEndElement();
                writer.WriteEndElement();

                writer.WriteStartElement("param");
                writer.WriteStartElement("value");
                writer.WriteElementString("string", Uri.EscapeUriString(_targetUri.ToString()));
                writer.WriteEndElement();
                writer.WriteEndElement();

                writer.WriteEndElement();
                writer.WriteEndElement();
            }
        }

var doc = new HtmlWeb().Load(url);
var linkTags = doc.DocumentNode.Descendants("link");
var linkedPages = doc.DocumentNode.Descendants("a")
                                  .Select(a => a.GetAttributeValue("href", null))
                                  .Where(u => !String.IsNullOrEmpty(u));

1- یک کلاس معمولی تنها می‌تواند از یک کلاس Abstract ارث بری کند ولی همان کلاس میتواند از چندین Interface ارث ببرد.

4- وقتی شما متدی را به کلاس Abstract اضافه می‌کنید، به طور خودکار به همه زیر کلاسها اعمال می‌شود؛ اما در Interface اگر متدی اضافه کنید باید در تمام زیر کلاسها آن را اعمال کنید . 

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp3.0</TargetFramework>
    <LangVersion>8.0</LangVersion>
    <Nullable>enable</Nullable>
  </PropertyGroup>
</Project>

    interface IDoStuff<TIn, TOut> where TIn : notnull where TOut : notnull
    {
        TOut DoStuff(TIn input);
    }

using System;
using System.Diagnostics.CodeAnalysis;

namespace ConsoleApp
{
    public class MyClass
    {
        private string _innerValue = string.Empty;

        [AllowNull]
        public string MyValue
        {
            get
            {
                return _innerValue;
            }
            set
            {
                _innerValue = value ?? string.Empty;
            }
        }
    }

    public class MyArray
    {
        // Result is the default of T if no match is found
        [return: MaybeNull]
        public static T Find<T>(T[] array, Func<T, bool> match)
        {
            //...
        }

        // Never gives back a null when called
        public static void Resize<T>([NotNull] ref T[]? array, int newSize)
        {
            //...
        }
    }

    public class MyString
    {
        // True when 'value' is null
        public static bool IsNullOrEmpty([NotNullWhen(false)] string? value)
        {
            //...
        }
    }

    public class MyVersion
    {
        // If it parses successfully, the Version will not be null.
        public static bool TryParse(string? input, [NotNullWhen(true)] out Version? version)
        {
            //...
        }
    }

    public class MyQueue<T>
    {
        // 'result' could be null if we couldn't Dequeue it.
        public bool TryDequeue([MaybeNullWhen(false)] out T result)
        {
            //...
        }
    }

    class MyPath
    {
        [return: NotNullIfNotNull("path")]
        public static string? GetFileName(string? path)
        {
            //...
        }
    }

    internal static class ThrowHelper
    {
        [DoesNotReturn]
        public static void ThrowArgumentNullException(ExceptionArgument arg)
        {
            //...
        }
    }

    public static class MyAssertionLibrary
    {
        public static void MyAssert([DoesNotReturnIf(false)] bool condition)
        {
            //...
        }
    }