using System.IO;
using System.Text.Encodings.Web;
using Microsoft.AspNetCore.Html;

namespace Sample
{
    /// <summary>
    /// Html Helper Extensions
    /// </summary>
    public static class HtmlHelperExtensions
    {
        /// <summary>
        /// Convert IHtmlContent/TagBuilder to string
        /// </summary>
        public static string GetString(this IHtmlContent content)
        {
            using (var writer = new StringWriter())
            {
                content.WriteTo(writer, HtmlEncoder.Default);
                return writer.ToString();
            }
        }
    }
}

Free System Design PDF (158 pages)

Here are some sample topics:
🔹 Why is Redis fast?
🔹 How to scale a website to support millions of users?
🔹 How does HTTPs work?
🔹 What happens when you type a URL into your browser?
🔹 How to avoid double charge?
🔹 Why is Kafka fast? 

public int Length { get; }
public int Count { get; }

public object this[int index] => throw null;
public object this[System.Index index] => throw null;

public object this[System.Range index] => throw null;
public object Slice(int start, int length) => throw null;

public class MyListPatternsCompatibleCollection
{
    private readonly List<int> _items = new();

    public int Length => _items.Count;

    public int this[Index index] => _items[index];

    public ReadOnlySpan<int> this[Range range]
        => CollectionsMarshal.AsSpan(_items)[range];

    public void Add(int item) => _items.Add(item);
}

 var collection = new MyListPatternsCompatibleCollection();
collection.Add(1);
collection.Add(2);
collection.Add(3);

_ = collection is [var head, .. var tail];

Last week, at ng-conf, the Angular team at Google provided the web developer world with an update on the state of Angular 2. They were joined on stage by a member of the TypeScript team, Jonathan Turner, to also announce that Angular 2 will be built using TypeScript. Jonathan then demoed a preview of the upcoming TypeScript 1.5 release via an Angular 2 sample application. 

var numbers1_CS11 = new[] { 1, 2, 3 };

var numbers1_CS_11 = new int[] { 1, 2, 3 };

int[] numbers1_CS12 = [ 1, 2, 3 ];

error CS9176: There is no target type for the collection expression.

Span<string> span1_CS11 = new string[] { "AC", "AL" };

Span<string> span1_CS12 = [ "AC", "AL" ];

ReadOnlySpan<string> readOnlySpan_CS12 = [ "Africa",  "Asia", "Europa"];

int[][] array2D_CS11 =
  {
    new int[] { 2002, 2006, 2010},
    new int[] { 2014, 2018},
    new int[] { 2022, 2026, 2030}
  };

int[][] array2D_CS12 =
  [
     [2002, 2006, 2010],
     [2014, 2018],
     [2022, 2026, 2030]
  ];

List<string> list_CS11 = new List<string> { "Item 1", "Item 2" };

List<string> list_CS12 = [ "Item 1", "Item 2" ];

// Before C#12
List<User> users = new List<User>();
// or
var users = new List<User>();
// or
List<User> user = new();

// C#12
List<User> users = [];

int[] numbers1_CS12 = [ 1, 2, 3 ];
int[] numbers2_CS12 = [ 4, 5, 6 ];

int[] allItems = [ ..numbers1_CS12, ..numbers2_CS12 ];

int[] allItems_CS11 = numbers1_CS12.Concat(numbers2_CS12).ToArray();

int[] join = [..a, ..b, ..c, 6, 5];

int[] a =[1, 2, 3];
Span<int> b = [2, 4, 5, 4, 4];
List<int> c = [4, 6, 6, 5];

List<int> join = [..a, ..b, ..c, 6, 5];

List<(string, int)> otherScores = [("Dave", 90), ("Bob", 80)];

(string name, int score)[] scores = [("Alice", 90), ..otherScores, ("Charlie", 70)];

        protected override void Dispose(bool disposing)
        {
            if (disposing)
            {
                if (this.wrappedConnection != null)
                    this.wrappedConnection.Dispose();
            }

            base.Dispose(disposing);
        }

using System;
using System.Configuration;
using System.Data;
using System.Data.Common;
using System.Data.Entity;
using System.Data.Entity.Infrastructure;
using System.Data.Entity.Migrations;
using System.Diagnostics;
using System.Linq;
using EFTracingProvider;

namespace Sample
{
    public class Person
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }

    public class Configuration : DbMigrationsConfiguration<MyContext>
    {
        public Configuration()
        {
            var className = this.ContextType.FullName;
            var connectionStringData = ConfigurationManager.ConnectionStrings[className];
            if (connectionStringData == null)
                throw new InvalidOperationException(string.Format("ConnectionStrings[{0}] not found.", className));

            TargetDatabase = new DbConnectionInfo(connectionStringData.ConnectionString, connectionStringData.ProviderName);
            AutomaticMigrationsEnabled = true;
            AutomaticMigrationDataLossAllowed = true;
        }

        protected override void Seed(MyContext context)
        {
            for (int i = 0; i < 7; i++)
                context.Users.Add(new Person { Name = "name " + i });

            base.Seed(context);
        }
    }

    public class MyContext : MyLoggedContext
    {
        public DbSet<Person> Users { get; set; }
    }

    public abstract class MyLoggedContext : DbContext
    {
        protected MyLoggedContext()
            : base(existingConnection: createConnection(), contextOwnsConnection: true)
        {
            var ctx = ((IObjectContextAdapter)this).ObjectContext;
            ctx.GetTracingConnection().CommandExecuting += (s, e) =>
            {
                Console.WriteLine("{0}\n", e.ToTraceString());
            };
        }

        private static DbConnection createConnection()
        {
            var st = new StackTrace();
            var sf = st.GetFrame(2); // Get the derived class Type in a base class static method
            var className = sf.GetMethod().DeclaringType.FullName;
            
            var connectionStringData = ConfigurationManager.ConnectionStrings[className];
            if (connectionStringData == null)
                throw new InvalidOperationException(string.Format("ConnectionStrings[{0}] not found.", className));

            if (!isEFTracingProviderRegistered())
                EFTracingProviderConfiguration.RegisterProvider();

            EFTracingProviderConfiguration.LogToFile = "log.sql";
            var wrapperConnectionString =
                string.Format(@"wrappedProvider={0};{1}", connectionStringData.ProviderName, connectionStringData.ConnectionString);
            return new EFTracingConnection { ConnectionString = wrapperConnectionString };
        }

        private static bool isEFTracingProviderRegistered()
        {
            var data = (DataSet)ConfigurationManager.GetSection("system.data");
            var providerFactories = data.Tables["DbProviderFactories"];
            return providerFactories.Rows.Cast<DataRow>()
                                         .Select(row => (string)row.ItemArray[1])
                                         .Any(invariantName => invariantName == "EF Tracing Data Provider");
        }
    }

    public static class Test
    {
        public static void RunTests()
        {
            Database.SetInitializer(new MigrateDatabaseToLatestVersion<MyContext, Configuration>());
            using (var ctx = new MyContext())
            {
                var users = ctx.Users.AsEnumerable();
                if (users.Any())
                {
                    foreach (var user in users)
                    {
                        Console.WriteLine(user.Name);
                    }
                }

                var rnd = new Random();
                var user1 = ctx.Users.Find(1);
                user1.Name = "test user " + rnd.Next();
                ctx.SaveChanges();
            }

        }
    }
}

 public class MyContext : MyLoggedContext

insert [dbo].[People]([Name])
values (@0)
select [Id]
from [dbo].[People]
where @@ROWCOUNT > 0 and [Id] = scope_identity()
-- @0 (dbtype=String, size=-1, direction=Input) = "name 0"

insert [dbo].[People]([Name])
values (@0)
select [Id]
from [dbo].[People]
where @@ROWCOUNT > 0 and [Id] = scope_identity()
-- @0 (dbtype=String, size=-1, direction=Input) = "name 1"

insert [dbo].[People]([Name])
values (@0)
select [Id]
from [dbo].[People]
where @@ROWCOUNT > 0 and [Id] = scope_identity()
-- @0 (dbtype=String, size=-1, direction=Input) = "name 2"

insert [dbo].[People]([Name])
values (@0)
select [Id]
from [dbo].[People]
where @@ROWCOUNT > 0 and [Id] = scope_identity()
-- @0 (dbtype=String, size=-1, direction=Input) = "name 3"

insert [dbo].[People]([Name])
values (@0)
select [Id]
from [dbo].[People]
where @@ROWCOUNT > 0 and [Id] = scope_identity()
-- @0 (dbtype=String, size=-1, direction=Input) = "name 4"

insert [dbo].[People]([Name])
values (@0)
select [Id]
from [dbo].[People]
where @@ROWCOUNT > 0 and [Id] = scope_identity()
-- @0 (dbtype=String, size=-1, direction=Input) = "name 5"

insert [dbo].[People]([Name])
values (@0)
select [Id]
from [dbo].[People]
where @@ROWCOUNT > 0 and [Id] = scope_identity()
-- @0 (dbtype=String, size=-1, direction=Input) = "name 6"

SELECT
[Extent1].[Id] AS [Id],
[Extent1].[Name] AS [Name]
FROM [dbo].[People] AS [Extent1]

SELECT
[Extent1].[Id] AS [Id],
[Extent1].[Name] AS [Name]
FROM [dbo].[People] AS [Extent1]

name 0
name 1
name 2
name 3
name 4
name 5
name 6

update [dbo].[People]
set [Name] = @0
where ([Id] = @1)
-- @0 (dbtype=String, size=-1, direction=Input) = "test user 1355460609"

-- @1 (dbtype=Int32, size=0, direction=Input) = 1

Looking at C# 12 Proposals and Beyond 

looking at parler specs and their architecture 

Looking Ahead to Entity Framework 7